Projection exposure apparatus and method

ABSTRACT

Two stages (WS 1 ), (WS 2 ) holding wafers can independently move between a positional information measuring section (PIS) under an alignment system ( 24   a ) and an exposing section (EPS) under a projection optical system (PL). The wafer exchange and alignment are performed on the stage (WS 1 ), during which wafer (W 2 ) is exposed on the stage (WS 2 ). A position of each shot area of wafer (WS 1 ) is obtained as a relative position with respect to a reference mark formed on the stage (WS 1 ) in the section (PIS). Relative positional information can be used for the alignment with respect to an exposure pattern when the wafer (WS 1 ) is moved to the section (EPS) to be exposed. Therefore, it is not necessary that a stage position is observed continuously in moving the stage. Exposure operations are performed in parallel by the two wafer stages (WS 1 ) and (WS 2 ) so as to improve the throughput.

This is a Continuation of application Ser. No. 08/980,315 filed Nov. 28,1997 now abandoned. The entire disclosure of the prior application ishereby incorporated by reference herein in its entirety.

This application claims benefit of Provisional applications; Ser. No.60/060,022 Sep. 25, 1997, and Ser. No. 60/059,989 filed Sep. 25, 1997,and Ser. No. 60/059,992 filed Sep. 25, 1997, and Ser. No. 60/060,677filed Sep. 25, 1997, and Ser. No. 60/060,076 filed Sep. 25, 1997.

FIELD OF THE INVENTION

The present invention relates to an exposure apparatus and an exposuremethod for exposing a sensitive substrate with a laser beam, an electronbeam and other charged particle beams. In particular, the presentinvention relates to an exposure apparatus and an exposure method, whichis used for producing semiconductor elements or liquid crystal displayelements by means of the photolithography process, and which exposes thesensitive substrate by projecting a pattern formed on a mask via aprojection optical system onto the sensitive substrate. Especially, thepresent invention relates to an exposure apparatus and an exposuremethod suitable for performing exposure and alignment of two substratesin parallel using two substrate stages.

BACKGROUND OF THE INVENTION

Various exposure apparatuses have been hitherto used, for example, whensemiconductor elements or liquid crystal display elements are producedby means of the photolithography step. At present, a projection exposureapparatus is generally used, in which an image of a pattern formed on aphotomask or reticle (hereinafter generally referred to as “reticle”) istransferred via a projection optical system onto a substrate(hereinafter referred to as “sensitive substrate”, if necessary) such asa wafer or a glass blade applied with a photosensitive material such asphotoresist on its surface. In recent years, a reduction projectionexposure apparatus (so-called stepper) based on the so-calledstep-and-repeat system is predominantly used as the projection exposureapparatus, in which a sensitive substrate is placed on a substrate stagewhich is movable two-dimensionally, and the sensitive substrate is movedin a stepwise manner (subjected to stepping) by using the substratestage to repeat the operation for successively exposing respective shotareas on the sensitive substrate with the image of the pattern formed onthe reticle.

Recently, a projection exposure apparatus based on the step-and-scansystem (scanning type exposure apparatus as described, for example, inJapanese Laid-Open Patent Publication No. 7-176468, corresponding toU.S. Pat. No. 5,646,413), which is obtained by applying modification tothe stationary type exposure apparatus such as the stepper, is also usedfrequently. The projection exposure apparatus based on the step-and-scansystem has, for example, the following merits. That is, (1) theprojection optical system is easily produced because a large field canbe exposed by using a smaller optical system as compared with thestepper, and a high throughput can be expected owing to the decrease innumber of shots because a large field is exposed. Further, (2) anaveraging effect is obtained owing to relative scanning for the reticleand the wafer with respect to the projection optical system, and therebyit is possible to expect improvement in distortion and depth of focus.Moreover, it is considered that the scanning type projection exposureapparatus will be predominantly used in place of the stepper, because alarge field will become essential in accordance with the increase in thedegree of integration of the semiconductor element, which is 16 M (mega)at present and will become 64 M for DRAM, 256 M, and 1 G (giga) infuture as the progress proceeds along with times.

With this type of projection exposure apparatus, alignment between thereticle and the wafer needs to be performed highly precisely prior toexposure. To carry out this alignment, the wafer is provided with aposition detecting mark (alignment mark) formed (or exposuretransferred) by a previous photolithographic process. By detecting theposition of this alignment mark, the exact position of the wafer (or acircuit pattern on the wafer) can be detected.

Alignment microscopes for detecting the alignment mark are roughlyclassified into the on-axis type for detecting the mark through aprojection lens, and the off-axis type for detecting the mark withoutallowing the detecting light pass through a projection lens. With regardto a projection exposure apparatus with an excimer laser light source,which would be predominant in this field, an alignment microscope of theoff-axis type is optimal. This is because the projection lens has beencorrected for chromatic aberration due to exposure light, so that theon-axis type cannot condense alignment light, or if it could, an errordue to chromatic aberration would be marked. An alignment microscope ofthe off-axis type, on the other hand, is provided separately from theprojection lens; therefore, free optical design is possible withoutregard for such chromatic aberration, and various alignment systems canbe used. For example, a phase contrast microscope or a differentialinterference microscope may also be used.

When the sensitive substrate is subjected to exposure by using thescanning type projection exposure apparatus, the so-called completepre-measurement control method has been carried out as follows asdescribed, for example, in Japanese Laid-Open Patent Publication No.6-283403 corresponding to U.S. Pat. No. 5,448,332. That is, alldetecting points included in one array provided on a front side in thescanning direction with respect to an exposure field are used as samplepoints. All values of focus positions at the sample points arepreviously measured before exposure, followed by the averaging processand the filtering process. The autofocus and the autoleveling mechanismsare controlled in an open manner during the exposure in consideration ofphase delay. Concurrently with the foregoing operation, an inclinationin the non-scanning direction is determined by means of the least squareapproximation method from the measured values of the focus positions atthe respective sample points in the one array described above to performthe leveling control in the non-scanning direction in accordance withthe open control.

Such a projection exposure apparatus is principally used as amass-production machine for semiconductor elements or the like.Therefore, the projection exposure apparatus necessarily required tohave a processing ability that how many sheets of wafers can besubjected to the exposure process for a certain period of time. That is,it is necessarily required for the projection exposure apparatus toimprove the throughput.

In this context, in the case of the projection exposure apparatus basedon the step-and-scan system described above, when a large field isexposed, the improvement in throughput is expected because the number ofshots to be exposed on the wafer is decreased as described above.However, since the exposure is performed during movement at a constantvelocity in accordance with synchronized scanning for the reticle andthe wafer, it is necessary to provide acceleration and decelerationareas before and after the constant velocity movement area. As a result,if a shot having a size equivalent to a shot size of the stepper isexposed, there is a possibility that the throughput is rather decreasedas compared with the stepper.

The outline of the flow of the process in such a projection exposureapparatus is as follows.

(1) At first, a wafer load step is performed, in which a wafer is loadedon a wafer table by using a wafer loader.

(2) Next, a search alignment step is performed, in which the position ofthe wafer is roughly detected by using a search alignment mechanism.Specifically, the search alignment step is performed, for example, onthe basis of the contour of the wafer, or by detecting a searchalignment mark on the wafer.

(3) Next, a fine alignment step is performed, in which the position ofeach of the shot areas on the wafer is accurately determined. Ingeneral, the EGA (enhanced global alignment) system is used for the finealignment step. In this system, a plurality of sample shots included inthe wafer are selected beforehand, and positions of alignment marks(wafer marks) affixed to the sample shots are successively measured.Statistical calculation based on, for example, the so-called leastsquare method is performed on the basis of results of the measurementand designed values of the shot array to determine all shot array dataon the wafer (see, for example, Japanese Laid-Open Patent PublicationNo. 61-44429 corresponding to U.S. Pat. No. 4,780,617). In this system,it is possible to determine the coordinate positions of the respectiveshot areas with high accuracy at a high throughput.

(4) Next, an exposure step is performed, in which the image of thepattern on the reticle is transferred onto the wafer via the projectionoptical system while successively positioning the respective shot areason the wafer to be located at exposure positions on the basis of thecoordinate positions of the respective shot areas having been determinedin accordance with the EGA system or the like described above and thepreviously measured baseline amount.

(5) Next, a wafer unload step is performed, in which the wafer on thewafer table having been subjected to the exposure process iswafer-unloaded by using a wafer unloader. The wafer unload step isperformed simultaneously with the wafer load step (1) described above inwhich the exposure process is performed. That is, a wafer exchange stepis constructed by the steps (1) and (5).

As described above, in the conventional projection exposure apparatus,the roughly classified four operations are repeatedly performed by usingone wafer stage, i.e., wafer exchange→search alignment→finealignment→exposure→wafer exchange.

The throughput THOR [sheets/hour] of such a projection exposureapparatus can be represented by the following expression (1) assumingthat the wafer exchange time is T1, the search alignment time is T2, thefine alignment time is T3, and the exposure time is T4.

THOR=3600/(T 1+T 2+T 3+T 4)  (1)

The operations of T1 to T4 are executed repeatedly and successively(sequentially) as in T1→T2→T3→T4→T1 . . . Accordingly, if the individualelements ranging from T1 to T4 involve high speeds, then the denominatoris decreased, and the throughput THOR can be improved. However, as forT1 (wafer exchange time) and T2 (search alignment time), the effect ofimprovement is relatively small, because only one operation is performedfor one sheet of wafer respectively. As for T3 (fine alignment time),the throughput can be improved if the sampling number of shots isdecreased in the case of the use of the EGA system, or if themeasurement time for a single shot is shortened. However, on thecontrary, the alignment accuracy is deteriorated due to shortened T3.Therefore, it is impossible to easily shorten T3.

On the other hand, T4 (exposure time) includes the wafer exposure timeand the stepping time for movement between the shots. For example, inthe case of the scanning type projection exposure apparatus based on,for example, the step-and-scan system, it is necessary to increase therelative scanning velocity between the reticle and the wafer in anamount corresponding to the reduction of the wafer exposure time.However, it is not allowed to increase the scanning velocity withoutconsideration because the synchronization accuracy is deteriorated.

With the apparatus using an off-axis alignment microscope, such as theprojection exposure apparatus with the excimer laser light source whichwould be predominant in this field, it is not easy to improve thecontrollability of the stage. With this type of projection exposureapparatus, there is need to precisely control the position of the waferstage, without Abbe's error, during exposure of the mask pattern throughthe projection optical system and during alignment, thereby to achievehighly precise superposition. For this purpose, it is necessary to set aconstitution in which the measuring axis of the laser interferometerpasses through the center of projection of the projection optical systemand the center of detection of the alignment microscope. Furthermore,neither the measuring axis passing through the center of projection ofthe projection optical system nor the measuring axis passing through thecenter of detection of the alignment microscope should be interrupted inthe moving range of the stage during exposure and in the moving range ofthe stage during alignment. To satisfy this requirement, the stagenecessarily becomes large in size.

Important conditions for such a projection exposure apparatus other thanthose concerning the throughput described above include (1) theresolution, (2) the depth of focus (DOF: Depth of Focus), and (3) theline width control accuracy. Assuming that the exposure wavelength is λ,and the numerical aperture of the projection lens is N.A. (NumericalAperture), the resolution R is proportional to λ/N.A., and the depth offocus (DOF) is proportional to λ/(N.A.)².

Therefore, in order to improve the resolution R (in order to decreasethe value of R), it is necessary to decrease the exposure wavelength λ,or it is necessary to increase the numerical aperture N.A. Especially,in recent years, semiconductor elements or the like have developed tohave high densities, and the device rule is not more than 0.2 μm L/S(line and space). For this reason, a KrF excimer laser is used as anillumination light source in order to perform exposure for the pattern.However, as described above, the degree of integration of thesemiconductor element will be necessarily increased in future.Accordingly, it is demanded to develop an apparatus provided with alight source having a wavelength shorter than that of KrF.Representative candidates for the next generation apparatus providedwith the light source having the shorter wavelength as described aboveinclude, for example, an apparatus having a light source of ArF excimerlaser, and an electron beam exposure apparatus. However, the case of theArF excimer laser involves numerous technical problems in that the lightis scarcely transmitted through a place where oxygen exists, it isdifficult to provide a high output, the service life of the laser isshort, and the cost of the apparatus is expensive. The electron beamexposure apparatus is inconvenient in that the throughput is extremelylow as compared with the light beam exposure apparatus. In reality, thedevelopment of the next generation machine, which is based on theprincipal viewpoint of the use of a short wavelength, does not proceedso well.

It is conceived to increase the numerical aperture N.A., as anothermethod to increase the resolution R. However, if N.A. is increased,there is a demerit that DOF of the projection optical system isdecreased. DOF can be roughly classified into UDOF (User Depth of Focus:a part to be used by user: for example, difference in level of patternand resist thickness) and the overall focus difference of the apparatusitself. Up to now, UDOF has contributed to DOF in a greater degree.Therefore, the development of the exposure apparatus has been mainlydirected to the policy to design those having a large DOF. Thosepractically used as the technique for increasing DOF include, forexample, modified illumination.

By the way, in order to produce a device, it is necessary to form, on awafer, a pattern obtained by combining, for example, L/S (line andspace), isolated L (line), isolated S (space), and CH (contact hole).However, the exposure parameters for performing optimum exposure differfor every shape of the pattern such as L/S and isolated line describedabove. For this reason, a technique called ED-TREE (except for CHconcerning a different reticle) has been hitherto used to determine, asa specification of the exposure apparatus, common exposure parameters(for example, coherence factor σ, N.A., exposure control accuracy, andreticle drawing accuracy) so that the resolution line width is within apredetermined allowable error with respect to a target value, and apredetermined DOF is obtained. However, it is considered that thefollowing technical trend will appear in future.

(1) In accordance with the improvement in process technology(improvement in flatness on the wafer), the difference in pattern levelwill be progressively lowered, and the resist thickness will beprogressively decreased. There will be a possibility that the UDOF maychange from an order of 1 μm→0.4 μm.

(2) The exposure wavelength changes to be short, i.e., g-ray (436nm)→i-ray (365 nm)→KrF (248 nm). However, investigation will be made foronly a light source based on ArF (193) in future. Further technicalhurdle is high. Thereafter, the progress will proceed to EB exposure.

(3) It is expected that the scanning exposure such as those based on thestep-and-scan system will be predominantly used for the stepper, inplace of the stationary exposure such as those based on thestep-and-repeat system. The step-and-scan system makes it possible toperform exposure for a large field by using a projection optical systemhaving a small diameter (especially in the scanning direction), in whichit is easy to realize high N.A. corresponding thereto.

In the background of the technical trend as described above, the doubleexposure method is reevaluated as a method for improving the limitingresolution. Trial and investigation are made such that the doubleexposure method will be used for KrF exposure apparatus and ArF exposureapparatus in future to perform exposure up to those having 0.1 μm L/S.In general, the double exposure method is roughly classified into thefollowing three methods.

(1) L/S's and isolated lines having different exposure parameters areformed on different reticles, and exposure is performed for each of themon an identical wafer under an optimum exposure condition.

(2) For example, when the phase shift method is introduced, L/S has ahigher resolution at an identical DOF as compared with the isolatedline. By utilizing this fact, all patterns are formed with L/S's byusing the first reticle, and L/S's are curtailed for the second reticleto form the isolated lines.

(3) In general, when the isolated line is used, a high resolution can beobtained with a small N.A. as compared with L/S (however, DOF isdecreased). Accordingly, all patterns are formed with isolated lines,and the isolated lines, which are formed by using the first and secondreticles respectively, are combined to form L/S's. The double exposuremethod described above has two effects of improvement in resolution andimprovement in DOF.

However, in the double exposure method, the exposure process must beperformed several times by using a plurality of reticles. Therefore,inconveniences arise in that the exposure time (T4) is not less thantwo-fold as compared with the conventional apparatus, and the throughputis greatly deteriorated. For this reason, actually, the double exposuremethod has not been investigated so earnestly. The improvement inresolution and depth of focus (DOF) has been hitherto made by means of,for example, the use of an ultraviolet exposure wavelength, modifiedillumination, and phase shift reticle.

However, when the double exposure method described above is used for theKrF and ArF exposure apparatuses, it is possible to realize exposurewith up to 0.1 μm L/S. Accordingly, it is doubtless that the doubleexposure method is a promising choice to develop the next generationmachine aimed at mass-production of DRAM of 256 M and 1 G. Therefore, ithas been expected to develop a new technique for improving thethroughput which is a task of the double exposure method as a bottleneckfor such a purpose.

In this context, if two or more operations of the four operations, i.e.,the wafer exchange, the search alignment, the fine alignment, and theexposure operations can be concurrently processed in parallel, it may bepossible to improve the throughput as compared with the case in whichthe four operations are sequentially performed. For this purpose, it ispremised that a plurality of substrate stages are provided. Theprovision of a plurality of substrate stages is known, which may beconsidered to be easy from a theoretical viewpoint. However, there arenumerous problems which should be solved in order to exhibit asufficient effect. For example, if two substrate stages each having asize equivalent to those of presently used substrate stages are merelyarranged and placed side by side, an inconvenience arises in that theinstallation area for the apparatus (so-called foot print) is remarkablyincreased, resulting in increase in cost of the clean room in which theexposure apparatus is placed. In order to realize highly accurateoverlay, it is necessary to execute alignment for the sensitivesubstrate on an identical substrate stage, and then execute positionaladjustment for the image of the pattern on the mask and the sensitivesubstrate by using a result of the alignment so that exposure is carriedout. Therefore, for example, if one of the two substrate stages ismerely exclusively used for exposure, and the other is merelyexclusively used for alignment, there is no real countermeasure.

Further, there have been hitherto the following necessities. That is,when two operations are concurrently processed in parallel to oneanother while independently controlling movement of two substratestages, then the movement should be controlled so that the both stagesdo not make contact with each other (prevention of interference), andthe operation performed on one of the stages does not affect theoperation performed on the other stage (prevention of disturbance).

Furthermore, in the case of the scanning type projection exposureapparatus, the order of exposure for respective shot areas on the waferW is determined, for example, by respective parameters of (1) to (4),i.e., (1) acceleration and deceleration times during scanning, (2)adjustment time, (3) exposure time, and (4) stepping time to adjacentshot. However, in general, the acceleration and the deceleration of thereticle stage give the rate-determining condition. Therefore, it is mostefficient that scanning is alternately performed for the reticle stagefrom one side to the other side and from the other side to one side inthe scanning direction, in synchronization with which scanning isalternately performed for the wafer in the direction opposite to thatfor the reticle stage (for this purpose, the wafer is subjected tostepping in an amount corresponding to one shot after exposure for oneshot).

However, when the conventional complete pre-measurement controldescribed above is performed (for example, Japanese Laid-Open PatentPublication No. 6-283403), it has been difficult to perform exposure inthe aforementioned most efficient order of exposure. That is, when ashot area in the vicinity of the center of the wafer is exposed, thecomplete pre-measurement control can be performed without any specialproblem. However, in the case of shot areas existing in the vicinity ofthe outer circumference of the wafer, and in the case of incompleteshots existing on the outer circumference, it is sometimes difficult toperform the complete pre-measurement control depending on the scanningdirection for such shot areas. In the present circumstances, it isinevitable to direct the scanning direction from the inside to theoutside of the wafer in order to perform complete pre-measurement. Forthis reason, the throughput has been consequently lowered.

Japanese Laid-Open Patent Publication No. 8-51069, corresponding to U.S.patent application Ser. No. 261,630 filed on Jun. 17, 1994, discloses astep-and-repeat apparatus comprising a plurality of wafer stations eachof which comprises a wafer position observing and tracking apparatus.The apparatus is provided, as the wafer station, with an image-formingstation and a characteristic measuring station, and each station has achuck for holding the wafer thereon. On the characteristic measuringstation, an inclination and a depth of a field is determined for eachfield of the wafer. The image-forming station is provided with animage-forming lens, and the image is printed on each field of the waferon which the characteristic has been measured in the measuringcharacteristic station. To measure the characteristic and to form animage in these stations are performed in parallel. This publicationdiscloses that therefore the throughput of this apparatus can be doubledcompared with a conventional stepper which performs the measurement ofcharacteristic and the formation of image in order. However, in thistype of apparatus, in order that the data concerning the wafer collectedon the measuring characteristic station are kept effective and accurateeven after the wafer has been transferred to the image-forming station,the wafer must be monitored continuously with an interferometer.

The present invention has been made under the circumstances as describedabove, and a first object of the invention is to provide a projectionexposure apparatus which makes it possible to further improve thethroughput.

A second object of the invention is to provide a projection exposuremethod which makes it possible to further improve the throughput.

A third object of the invention is to provide a projection exposureapparatus which makes it possible to improve the throughput byconcurrently processing, for example, the exposure operation and thealignment operation in parallel to one another, miniaturize a substratestage, and reduce the weight of the substrate stage.

A fourth object of the invention is to provide a projection exposuremethod which makes it possible to improve the throughput, miniaturize astage, and reduce the weight of the stage.

A fifth object of the invention is to provide a projection exposureapparatus which makes it possible to further improve the throughput andavoid any mutual influence of disturbance between the both stages.

A sixth object of the invention is to provide a projection exposureapparatus which makes it possible to further improve the throughput andavoid any mutual interference between the both stages.

A seventh object of the invention is to provide a projection exposuremethod which makes it possible to further improve the throughput andavoid any mutual influence of disturbance between the both stages.

An eighth object of the invention is to provide a projection exposuremethod which makes it possible to further improve the throughput andavoid any mutual interference between the both stages.

A ninth object of the invention is to provide a projection exposureapparatus which makes it possible to perform highly accuratefocus/leveling control while further improving the throughput.

A tenth object of the invention is to provide a projection exposuremethod which makes it possible to perform highly accurate focus/levelingcontrol while further improving the throughput.

An eleventh object of the invention is to provide a projection exposuremethod which makes it possible to perform highly accurate focus/levelingcontrol while further improving the throughput even when EGA isperformed for conducting positional adjustment with respect to a mask onthe basis of an arrangement of sample shot areas.

A twelfth object of the invention is to provide a projection exposureapparatus which makes it possible to perform highly accuratefocus/leveling control while further improving the throughput, such thatfocus information concerning those disposed at the inside, which hasbeen impossible to be subjected to pre-measurement when shot areas inthe vicinity of outer circumference of a sensitive substrate areexposed, is used as pre-measurement data for focus control.

A thirteenth object of the invention is to provide a scanning exposuremethod which makes it possible to perform highly accurate focus/levelingcontrol while further improving the throughput.

A fourteenth object of the invention is to provide an exposure methodcapable of improving throughput and determining the size of thesubstrate stage regardless of the baseline amount.

SUMMARY OF THE INVENTION

If a plurality of actions among the aforementioned three actions, i.e.,wafer replacement (including search alignment), fine alignment andexposure, can be performed in parallel even partially, throughput may beimproved compared with the sequential execution of these actions. Thepresent invention has been devised in this view and for overcoming theinconveniences of the conventional art.

According to the first aspect of the present invention, there isprovided an exposure apparatus for exposing a plurality of areas (SA)divided on a sensitive substrate (W1, W2) respectively with apredetermined pattern, the exposure apparatus comprising;

a plurality of stages (WS1, WS2), each holding a sensitive substrate(W1, W2) thereon, while moving independently between a positionalinformation measuring section (PIS) wherein positional information ofthe respective divided areas on the sensitive substrate are measured andan exposure section (EPS). The measurement of the positional informationon the respective divided areas (shot areas (SA)) on the sensitivesubstrate is performed on the positional information measuring section(PIS), while the exposure of the respective divided areas is performedon the exposure section (EPS). Since the measurement and the exposureare performed in parallel, the throughput is remarkably improvedcompared to a conventional exposure apparatus wherein the process stepsin these sections are performed sequentially. In order for the inventiveexposure apparatus to keep accurate the positional information, such aspositions in a directions of X, Y and Z of each area, measured in thepositional information measuring section, each stage (WS1, WS2) has areference mark (MK1, MK2, MK3) for determining a relative position ofeach divided area on the sensitive substrate on the stage. The alignmentof each divided area on the sensitive substrate is performed in theexposure section using the relative position of each divided area withrespect to the reference mark measured in the positional informationmeasuring section. Accordingly, it is sufficient for each of theposition measuring system (such as interferometers) for measuringposition of the stage positioned on the positional information measuringsection and the position measuring system (such as interferometers) formeasuring position of the stage positioned on the exposure section, toindependently measure the stage position only in one section. It is notnecessary for one of the position measuring systems to monitor theposition of one stage during the movement of the stage between the twosections. Further, there is no need to transmit data between theposition measuring systems.

The exposure apparatus further may comprise positional informationdetecting systems in the positional information measuring section andthe exposing section, respectively. The positional information detectingsystems may measure or determine the position of each divided area ofthe sensitive substrate with respect to the reference mark. When theexposure apparatus is a projection exposure apparatus, the positionalinformation detecting system in the positional information measuringsection may an alignment system (24 a, 24 b) and a detection system(130) for detecting the position of the surface of the sensitivesubstrate, and the positional information detecting system in theexposure section may be a detector for detecting the marks through theprojection optical system. The exposure apparatus may further comprise astoring apparatus (91) for storing positional information of eachdivided area on the sensitive substrate which has been determined in thepositional information measuring section.

According to the second aspect of the present invention, there isprovided a projection exposure apparatus for exposing a sensitivesubstrate (W1, W2) by projecting a pattern formed on a mask (R) througha projection optical system (PL) onto the sensitive substrates,characterized by having:

a first substrate stage (WS1) which is movable on a two-dimensionalplane while holding a sensitive substrate (W1), the first substratestage having a reference mark formed thereon;

a second substrate stage (WS2) which is movable independently from thefirst substrate stage (WS1) on the same plane as that for the firstsubstrate stage (WS1) while holding a sensitive substrate (W2), thesecond substrate stage having a reference mark formed thereon;

at least one mark detecting system (for example, 24 a) provided apartfrom the projection optical system (PL), for detecting reference mark onthe substrate stage (WS1, WS2) or a mark on the sensitive substrate(WS1, WS2) held on the substrate stage (WS1, WS2); and

a controller (90) for controlling operations of the both stages (WS1,WS2) so that one of the first and second substrate stages (WS1 or WS2)performs a mark-detecting operation effected by the mark detectingsystem (24 a), while the other stage (WS2 or WS1) performs an exposureoperation.

According to the projection exposure apparatus, the controller controlsthe operations of the both stages (WS1, WS2) so that the one of thestages of the first substrate stage and the second substrate stageperforms the mark-detecting operation effected by the mark detectingsystem, during which the exposure operation is performed on the otherstage. Accordingly, the detecting operation for the mark on thesensitive substrate held on the one substrate stage can be processedconcurrently with the exposure operation for the sensitive substrateheld on the other substrate stage. Therefore, the operationcorresponding to the time T2 and the time T3 explained above can beprocessed concurrently with the operation corresponding to the time T4.Thus, it is possible to improve the throughput as compared with theconventional sequential process which requires the time (Ti+T2+T3+T4).

In this projection exposure apparatus, it is still more desirable thatwhen the projection exposure apparatus further comprises a transportsystem (180 to 200) for delivering the sensitive substrate (W1, W2) withrespect to the first and second substrate stages (WS1 and WS2), then thecontroller (90) controls the operations of the both stages (WS1, WS2) sothat one of the substrate stages (WS1 or WS2) performs the delivery ofthe sensitive substrate with respect to the transport system (180 to200) and the mark-detecting operation effected by the mark detectingsystem (24 a), during which the other stage (WS2 or WS1) performs theexposure operation effected by the projection optical system (PL). Insuch an arrangement, the operation corresponding to the time T1, thetime T2, and the time T3 explained above can be performed by the onesubstrate stage, and the operation corresponding to the time T4 can beperformed by the other substrate stage. Accordingly, it is possible tofurther improve the throughput.

In the projection exposure apparatus, at least one mark detecting systemsuch as alignment system may be provided separately from the projectionoptical system. However, for example, when two mark detecting systemsare provided separately from the projection optical system, it is alsopreferable, that the two mark detecting systems (24 a, 24 b) arearranged on both sides of the projection optical system (PL) along apredetermined direction; and the controller (90) is operated such thatthe reference mark on the first substrate stage (WS1) or the mark on thesensitive substrate (W1) held on the first substrate stage (WS1) isdetected by using the one mark detecting system (24 a), and thereference mark on the second substrate stage (WS2) or the mark on thesensitive substrate (W2) held on the second substrate stage (WS2) isdetected by using the other mark detecting system (24 b). In thisembodiment as described above, the sensitive substrate on the onesubstrate stage may be exposed by using the projection optical systemlocated at the center (exposure operation), during which the sensitivesubstrate on the other substrate stage may be subjected to the markdetection by using the one mark detecting system (alignment operation).When the exposure operation is changed to the mark detecting operation,then the one substrate stage having been located under the projectionoptical system can be easily moved to the position of the other markdetecting system, and the other substrate stage having been located atthe position of the one mark detecting system can be easily moved to theposition under the projection optical system, only by moving the twosubstrate stages along the predetermined direction toward the other markdetecting system. By doing so, it is possible to alternately use the twomark detecting systems.

According to the third aspect of the present invention, there isprovided a projection exposure method for exposing a sensitive substrate(W1, W2) by projecting a pattern formed on a mask (R) through aprojection optical system (PL) onto the sensitive substrates,characterized by:

preparing two substrate stages (WS1, WS2) each of which is movableindependently on a two-dimensional plane while holding a sensitivesubstrate (W1, W2); and

performing, by using one stage (WS1 or WS2) of the two substrate stages(WS1, WS2), at least one of an exchange operation for the sensitivesubstrate and a detecting operation for a mark on the one stage or onthe sensitive substrate held on the one stage, while executing anexposure operation for the sensitive substrate by using the other stage(WS2 or WS1) of the two substrate stages.

According to the projection exposure method, at least one of theoperation corresponding to the time T1 and the operation correspondingto the time (T2+T3) explained above is performed on the one substratestage, during which the operation corresponding to the time T4 isperformed on the other substrate stage concurrently therewith.Accordingly, it is possible to improve the throughput as compared withthe conventional sequential process which requires the time(Ti+T2+T3+T4). Especially, when the operation corresponding to the time(T1+T2+T3) is performed by the one stage, during which the operationcorresponding to the time T4 is performed by the other stageconcurrently therewith, then it is possible to further improve thethroughput.

In this aspect, the respective operations performed on the two substratestage are not necessarily completed at the same time. However, it isalso preferable that the operations of the two substrate stages arechanged to one another at a point of time of completion of theoperations of the two substrate stages. Accordingly, among the twostages, one stage, on which the operation is completed earlier, issubjected to a waiting mode, and the operations are changed to oneanother at the point of time of completion of the operation of the otherstages. The waiting time may behave as a factor to lower the throughput.Therefore, it is desirable that the contents of the operationsconcurrently processed on the two substrate stages are divided so thatthe waiting time is decreased as short as possible.

According to the fourth aspect of the present invention, there isprovided a method for exposing a sensitive substrate (W) by projecting apattern formed on a mask (R) through a projection optical system (PL)onto the sensitive substrates, characterized by:

preparing two substrate stages (WS1, WS2) independently movable in thesame plane while each holding a sensitive substrate (W);

exposing the sensitive substrate (W) held on one of the two substratestages (WS1 or WS2) with the pattern image of the mask (R) through theprojection optical system (PL);

measuring the positional relation between an alignment mark on thesensitive substrate (W) held on the other of the two substrate stages(WS2 or WS1) and a reference point on the other stage (WS2 or WS1)during exposure of the sensitive substrate (W) held on the one substratestage (WS1 or WS2);

detecting the positional deviation of the reference point on the othersubstrate stage from a predetermined reference point in a projectionarea of the projection optical system and the coordinate position of theother substrate stage, with the reference point on the other substratestage being positioned in the projection area, after completion ofexposure of the sensitive substrate held on the one substrate stage; and

controlling the movement of the other substrate stage on the basis ofthe detected positional relation, the detected positional deviation andthe detected coordinate position to perform alignment between thesensitive substrate held on the other stage and the pattern image of themask.

According to the projection exposure method, while the sensitivesubstrate (W) held on the one substrate stage (WS1 or WS2) of the twosubstrate stages (WS1, WS2) is being exposed with the pattern image ofthe mask (R) through the projection optical system (PL), {circle around(1)} the positional relation between the alignment mark on the sensitivesubstrate (W) held on the other substrate stage (WS2 or WS1) of the twosubstrate stages and the reference point on the other stage (WS2 or WS1)is measured. As noted from this, the exposure action on the onesubstrate stage side and the alignment action on the other substratestage side (measurement of the positional relation between the alignmentmark on the sensitive substrate held on the other substrate stage andthe reference point on the other substrate stage) can be performed inparallel. Thus, throughput can be improved in comparison withconventional technologies by which these actions were performedsequentially.

After exposure of the sensitive substrate held on the one substratestage, {circle around (2)} the positional deviation of the referencepoint on the other substrate stage from the predetermined referencepoint in the projection area of the projection optical system (PL) and{circle around (3)} the coordinate position of the other substrate stageat the time of detecting the positional deviation are detected, with thereference point on the other substrate stage (WS2 or WS1) beingpositioned in the projection area. Then, the movement of the othersubstrate stage (WS2 or WS1) is controlled on the basis of the detectedpositional relation {circle around (1)}, the detected positionaldeviation {circle around (2)} and the detected coordinate position{circle around (3)} to perform alignment between the sensitive substrateheld on the other stage and the pattern image of the mask.

Thus, it presents no disadvantages whether the interferometer (orcoordinate system) for managing the position of the substrate stage atthe time of detecting the positional relation {circle around (1)}between the predetermined reference point on the other substrate stageand the alignment mark on the sensitive substrate is the same as ordifferent from the interferometer (or coordinate system) for managingthe position of the stage during the detection of the positionaldeviation {circle around (2)} and during the detection of the coordinateposition of the substrate stage {circle around (3)}. Regardless ofwhether these two interferometers are different, the alignment of thepattern image of the mask with the sensitive substrate placed on theother substrate stage can be performed highly accurately. This meansthat there is no need to successively measure the positions of the stageby one interferometer during the alignment operation, the movementoperation from an alignment position to the exposure position and theexposure operation.

Thus, when an off-axis alignment system (a detector for detecting analignment mark is not directly below the projection optical system) isused as a mark detection system for detecting the alignment mark, forexample, it becomes unnecessary to measure the positional relationbetween the predetermined reference point in the projection area of theprojection optical system (the center of projection of the pattern imageof the mask) and the center of detection of the alignment system, thatis, unnecessary to measure the baseline amount. As a result, whateverdistance exists between the projection optical system and the alignmentsystem produces no disadvantage. Thus, the size of the substrate stagecan be design irrespective of the baseline amount. Even if the substratestage becomes small in size or light in weight, no disadvantage willemerge, and mark position measurement and pattern projection by exposurethrough the projection optical system can be carried out for the entiresurface of the sensitive substrate. In this case, no influence ofchanges in the baseline amount is exerted.

According to the fifth aspect of the present invention, there isprovided a projection exposure apparatus for exposing a sensitivesubstrate (W) by projecting a pattern through a projection opticalsystem (PL) onto the sensitive substrates, comprising:

a first substrate stage (WS1), on which a reference mark is formed,moving in a two-dimensional plane while holding a sensitive substrate(W);

a second substrate stage (WS2), on which a reference mark is formed,moving in the same plane in which the first substrate stage (WS1) movesindependently of the first substrate stage (WS1) while holding asensitive substrate (W);

a mark detecting system (WA), provided apart from the projection opticalsystem (PL), for detecting the reference mark on the substrate stage(WS1, WS2) or a mark on the sensitive substrate (W) held on the stage;

an interferometer system (26) for measuring the two-dimensionalpositions of the first substrate stage and the second substrate stage;

a moving device (201, 22) for moving each stage between a predeterminedfirst position in a stage moving range during exposure during which thesensitive substrate held on the stage is exposed through the projectionoptical system, and a predetermined second position in a stage movingrange during mark detecting during which the mark on the stage or themark on the sensitive substrate held on the stage is detected by themark-detecting system; and

controller (28) for controlling the actions of the first substrate stageand the second substrate stage while monitoring the measured values ofthe interferometer system (26) so that during exposure of the sensitivesubstrate held on one of the first substrate stage and the secondsubstrate stage, a mark detecting action by the mark detecting system(WA) is performed on the other of the first substrate stage and thesecond substrate stage, and then controlling the moving device (201, 22)to interchange the positions of the one substrate stage and the othersubstrate stage.

According to the above constitution, the controller (28) controls theactions of the two stages while monitoring the measured values of theinterferometer system (26) so that during exposure of the sensitivesubstrate held on one stage of the two stages, a mark detecting actionby the mark detecting system (for example, an alignment system) (WA) isperformed on the other-stage, and then controls the moving device(201,221) to interchange the position of the one stage with the position ofthe other stage. This parallel execution of the exposure action on theone stage side and the alignment action on the other stage side enablesthroughput to be improved. Also, if the sensitive substrate is replacedon the substrate stage at the second position after interchange of thepositions, actions of the two stages are interchanged, whereby duringexposure of the sensitive substrate held on the other stage, a markdetecting action by the mark detecting system (for example, thealignment system) (WA) can be performed on the one stage.

According to the projection exposure apparatus, the interferometersystem (26) may has the first measuring axis (Xe) and the secondmeasuring axis (Ye) intersecting each other perpendicularly at thecenter of projection of the projection optical system (PL), and thethird measuring axis (Xa) and the fourth measuring axis (Ya)intersecting each other perpendicularly at the center of detection ofthe mark detecting system (WA). It is desirable that the controller (28)resets the measuring axes (Xe, Ye, Xa, Ya) of the interferometer system(26) in interchanging the positions of the one stage and the otherstage. By means of constituting the interferometer system and thecontroller in this manner, since the interferometer system (26) has thefirst measuring axis (Xe) and the second measuring axis (Ye)intersecting each other perpendicularly at the center of projection ofthe projection optical system (PL), and the third measuring axis (Xa)and the fourth measuring axis (Ya) intersecting each otherperpendicularly at the center of detection of the mark detecting system(alignment system) (WA), the positions of the substrate stages (WS1,WS2) can be managed precisely without Abbe's error both during exposureof the sensitive substrate with the pattern through the projectionoptical system and during detection of the position detecting mark bythe mark detecting system. Furthermore, the controller (28) resets themeasuring axes (Xe, Ye, Xa, Ya) of the interferometer system (26) ininterchanging the positions of the one stage and the other stage. Duringposition interchange, the measuring axes of the interferometer systemthat has managed the positions of the substrate stages until then may beinterrupted. Even in this case, it suffices to predetermine thepositions at which to reset the measuring axes (Xe, Ye, Xa, Ya) of theinterferometer system (26). After resetting, the positions of the firstand second substrate stages can be managed using the measured values ofthe reset measuring axes.

According to the sixth aspect of the present invention, there isprovided an exposure apparatus for exposing a sensitive substrates (W)by projecting a pattern on the sensitive substrate through a projectionoptical system (PL) comprising:

a first substrate stage (WS1), on which a reference mark is formed, formoving in a two-dimensional plane while holding a sensitive substrate(W);

a second substrate stage (WS2), on which a reference mark is formed, formoving in the same plane in which the first substrate stage (WS1)independently of the first substrate stage while holding a sensitivesubstrate (W);

a mark detecting system (WA) provided apart from the projection opticalsystem (PL), for detecting the reference mark formed on the substratestage or an alignment mark on the sensitive substrate held on the stage;

an interferometer system (26) for measuring the two-dimensionalpositions of the first substrate stage and the second substrate stage;

a moving device (201, 221) for moving each stage among three locations,i.e., a predetermined first position in a stage moving range duringexposure during which the sensitive substrate (W) held on the stage isexposed through the projection optical system (PL), a predeterminedsecond position in a stage moving range during alignment during whichthe mark on the stage or the mark on the sensitive substrate held on thestage is detected by the mark detecting system (WA), and a thirdposition at which the sensitive substrate is passed on between the stageand an external substrate carrier mechanism; and

controller (28) for controlling the first and second substrate stages(WS1, WS2) and the moving device (201, 221) so that while the positionof one of the first (WS1) and second (WS2) substrate stages is beingmanaged by the interferometer system (26) and the sensitive substrate(W) held on the one stage is being exposed with the pattern through theprojection optical system (PL), the replacement of the sensitivesubstrate (W), and an alignment action for measuring the positionalrelation between the alignment mark on the sensitive substrate (W) and areference mark on the other stage based on the results of detection bythe mark detecting system (WA) and the measured values by theinterferometer system (26) are sequentially performed on the other ofthe first and second substrate stages; and for controlling the twostages and the moving device so that after the actions on the two stagesare both completed, the actions to be performed on the two stages areinterchanged.

According to the exposure apparatus, the controller controls the twosubstrate stages (WS1, WS2) and the moving device (201, 221) so thatwhile the position of the one substrate stage is being managed by theinterferometer system and the sensitive substrate held on the onesubstrate stage is being exposed with the pattern through the projectionoptical system, the replacement of the sensitive substrate (W), and analignment action for measuring the positional relation between thealignment mark on the sensitive substrate (W) after replacement and thereference mark on the other stage based on the detection results of themark detecting system (WA) and the measured values by the interferometersystem (26) are sequentially performed on the other substrate stage.Since the exposure action on the one substrate stage side and thereplacement of the sensitive substrate as well as the alignment actionon the other stage side are thus performed in parallel, throughput canbe further improved. In this case, the sensitive substrate is replacedat the third position different from the first or second position. Sincethis position of replacement is different from the positions of the markdetecting system(for example, an alignment system) and the projectionoptical system, the disadvantage that the mark detecting system and theprojection optical system impede the replacement of the sensitivesubstrate does not occur.

The controller also controls the two stages and the moving device sothat after the actions of the two stages are both completed, the actionsto be performed on the two stages are interchanged. Thus, aftercompletion of the actions on the two stages, the Sensitive substrateheld on the other stage is exposed successively, and during thisexposure, the mark detecting action by the mark detecting system (WA)can be performed on the one stage in parallel.

In this case, an electronic lens barrel, for example, may be used as theprojection optical system, and the pattern may be directly drawn on thesensitive substrate with an electron beam. However, a mask (R) with thepattern formed thereon may be further provided, and the pattern imageformed on the mask (R) via the projection optical system (PL) may beprojected onto the sensitive substrates (W) on the first substrate stage(WS1) and the second substrate stage (WS2).

In the exposure apparatus of the invention, it is desirable that theinterferometer system (26) has a first measuring axis (Xe) and a secondmeasuring axis (Ye) intersecting each other perpendicularly at thecenter of projection of the projection optical system (PL), and a thirdmeasuring axis (Xa) and a fourth measuring axis (Ya) intersecting eachother perpendicularly at the center of detection of the mark detectingsystem (WA), and the controller (28) resets the first and secondmeasuring axes (Xe and Ye) of the interferometer system (26) in movingeach of the two stages (WS1, WS2) to the first position, and resets thethird and fourth measuring axes (Xa and Ya) of the interferometer system(26) in moving each of the two stages (WS1, WS2) to the second position.

By means of constituting the interferometer and the controller, sincethe interferometer system (26) has the first measuring axis (Xe) and thesecond measuring axis (Ye) intersecting each other perpendicularly atthe center of projection of the projection optical system (PL), and thethird measuring axis (Xa) and the fourth measuring axis (Ya)intersecting each other perpendicularly at the center of detection ofthe mark detecting system (WA), the positions of the substrate stages(WS1, WS2) can be managed precisely without Abbe's error both duringexposure of the sensitive substrate with the pattern through theprojection optical system and during detection of the position detectingmark by the mark detecting system. Furthermore, the controller (28)resets the first and second measuring axes (Xe and Ye) of theinterferometer system (26) in moving each of the two stages (WS1, WS2)to the first position, and resets the third and fourth measuring axes(Xa and Ya) of the interferometer system (26) in moving each of the twostages (WS1, WS2) to the second position. Thus, prior to the start ofexposure and the start of aligning measurement for each substrate stage,it is possible to rest the measuring axes that are required for therespective actions. Until then, the measuring axes of the interferometersystem that has managed the positions of the respective substrate stagesmay be interrupted. After resetting, however, the positions of the twostages at the time of exposure and alignment can be managed using themeasured values of the reset measuring axes.

In the exposure apparatus of the invention, it is desirable to furtherprovide mark position detector (52A, 52B) for detecting the relativepositional relation between the center of projection of the patternimage of the mask (R) formed by the projection optical system and thereference mark on the stage via the mask (R) and the projection opticalsystem (PL). By so doing, the positional relation between the center ofprojection of the pattern image of the mask (R) and the reference markon the substrate stage can be detected by the mark position detector(52A, 52B) via the mask (R) and the projection optical system (PL) whenthe substrate stages (WS1, WS2) are positioned at a position at whichthe positional relation between the predetermined reference mark on thesubstrate stage and the center of projection of the mask pattern imagecan be detected in the projection area of the projection optical system(PL). In this case, it is desirable that the position at which thepositional relation between the predetermined reference mark on thesubstrate stage and the center of projection of the mask pattern imagecan be detected in the projection area of the projection optical system(PL) be set as the first position, and the first and second measuringaxes be reset at this position.

In the exposure apparatus, each of the substrate stages (WS1, WS2) mayhave a stage body (WS1 a, WS2 a), and a substrate holding member (WS1 b,WS2 b) detachably mounted on the body (WS1 a, WS2 a) for holding thesubstrate, a reflecting surface for an interferometer may be provided onthe side surface of the substrate holding member (WS1 b, WS2 b), and areference mark (WM, RM) may be formed on the upper surface of thesubstrate holding member. When the exposure apparatus has suchconstitutions, the moving device (201, 221) may move the substrateholding member among the respective locations mentioned earlier insteadof the substrate stage.

In the above cases, the moving device may be of any type which moves thesubstrate stage or the substrate holding member among the threelocations, i.e., the first position, the second position and the thirdposition (or between the first and second positions), without monitoringthe measured values by the interferometer. For instance, the movingdevice may be composed of a robot arm (201, 221).

In the exposure apparatus, a fixed mirror serving as a reference formeasurement by the interferometer may be located at any place. Fixedmirrors (14X, 14Y; 18X, 18Y) serving as a reference for measurement bythe interferometer may be attached to the projection optical system (PL)and the mark detecting system (WA), respectively. In this case, comparedwith the fixed mirrors existing at other places, an error minimallyoccurs in the results of measurement under the influence of positionalchanges of the fixed mirrors over time or the influence of positionalchanges of the fixed mirrors associated with vibrations of theapparatus.

In the exposure apparatus, only two stages, the first substrate stageand the second substrate stage, are provided. However, at least oneother substrate stage movable independently of the two substrate stagesin the same plane as for these stages while holding a sensitivesubstrate may be further provided in addition to the first substratestage (WS1) and the second substrate stage (WS2).

According to the seventh aspect of the present invention, there isprovided a projection exposure apparatus for exposing a plurality ofshot areas divided on a sensitive substrate (W1, W2) by projecting animage of a pattern formed on a mask (R) via a projection optical system(PL) onto each of the shot areas, characterized by comprising:

a first substrate stage (WS1) which is movable on a two-dimensionalplane while holding a sensitive substrate (W1);

a second substrate stage (WS2) which is movable independently from thefirst substrate stage (WS1) on the same plane as that for the firstsubstrate stage (WS1) while holding a sensitive substrate (W2);

a positional information detecting system (for example, 24 a, 130) fordetecting the positional information of at least one shot area of thesensitive substrate (W1 or W2) held on the substrate stage (WS1 or WS2)provided apart from the projection optical system (PL);

substrate-driving systems (LS) provided for the first substrate stage(WS1) and the second substrate stage (WS2) respectively, for adjustingsurface positions of the sensitive substrates (W1 or W2) held on thestages (WS1 or WS2); and

a controller (90) for controlling the two stages (WS1, WS2) so that apositional information detecting operation based on the use of thepositional information detecting system (24 a, 130) is performed for onestage (for example, WS1) of the first substrate stage (WS1) and thesecond substrate stage (WS2), during which an exposure operation basedon the use of the projection optical system (PL) is performed for theother of the stages (for example WS2), thereafter controlling one of thestages (WS1) so that the exposure operation based on the use of theprojection optical system (PL) is performed for the one of the stages(WS1), and controlling the substrate-driving system (LS1) for the one ofthe stages (WS1) to perform an alignment of the shot area in exposure,using information on a surface position of the shot area resulted fromthe positional information detection.

According to the exposure apparatus, the two stages are controlled bythe controller so that the detection of positional information based onthe use of the positional information detecting system is performed forone of the stages of the first substrate stage and the second substratestage, during which the exposure operation is performed by using theprojection optical system for the other of the stages. Accordingly, themark-measuring operation for the one of the stages is processedconcurrently in parallel to the exposure operation for the other of thestages. Thus, it is possible to contemplate improvement in throughput ascompared with the conventional technique in which these operations havebeen sequentially performed. Further, after completion of the concurrentprocess of the mark-measuring operation for one of the stages and theexposure operation for the other stage, the controller controls the oneof the stages so that the exposure operation based on the use of theprojection optical system is performed for the one of the stages, andthe controller controls the substrate-driving system for the one of thestages on the basis of the detection result obtained by usinginformation of the surface position of the shot area during thedetection of the positional information for the one of the stages.Accordingly, during the exposure operation for the one of the stages,the substrate-driving system for the one of the stages is controlledusing the surface position (Z-directional position) obtained during thedetection of the positional information so that the surface position ofthe sensitive substrate can be quickly driven into a position near tothe image formation plane of the projection optical system.

In the exposure apparatus, the positional information detecting systemmay comprise at least one alignment system (24 a) for measuring a markon the sensitive substrate held on the substrate stage and a firstdetecting system (130) for detecting positional information of a surfaceof the sensitive substrate during measurement operation of the markbased on the use of the alignment system. Further, the positionalinformation detecting system may be provided with a second detectingsystem (132) for detecting positional information of a surface of thesensitive substrate during exposure operation based on the use of theprojection optical system. The controller (90) may control the twostages so that the detection by using the positional informationdetecting system for one of the stages of the first substrate stage andthe second substrate stage is performed, during which the exposureoperation based on the use of the projection optical system is performedfor the other of the stages. After that, the controller may control theone of the stages so that the exposure operation based on the use of theprojection optical system is performed for the one of the stages. Andalso, the controller may control the substrate-driving system (LS) forthe one stage on the basis of the detection result obtained by using thefirst detecting system during the mark-measuring operation for the onestage and the detection result obtained by using the second detectingsystem during the exposure operation for the one stage to perform analignment in the exposure of the shot area. The substrate-driving systemcan be further adjusted finely on the basis of the detection resultobtained by using the second detecting system so that the surface of thesensitive substrate coincides with the image formation plane. Therefore,it is possible to perform quick and highly accurate focus/levelingcontrol.

It is desirable that the projection exposure apparatus is a scanningtype projection exposure apparatus (for example, a step-and-scan typeexposure apparatus) for exposing sensitive substrates with an image of apattern formed on a mask (R) by moving the sensitive substrate in ascanning direction with respect to an exposure area (IF) which isconjugate to an illumination area (IA) illuminated with an illuminationlight beam, in synchronization with movement of the mask in the scanningdirection with respect to the illumination area. In this case, thecontroller (90) controls the two stages so that the detection by usingthe positional information detecting system for one stage of the firstsubstrate stage and the second substrate stage is performed, duringwhich the exposure operation based on the use of the projection opticalsystem is performed for the other of the stages. After that, when theone stage is controlled so that the exposure operation based on the useof the projection optical system is performed for the one stage, uponexposure for shot areas in the vicinity of outer circumference which areset to be subjected to scanning from the outside to the inside of thesensitive substrate with respect to the exposure area (IF), of aplurality of shot areas on the sensitive substrate held on the one ofthe stages, the controller may control the substrate-driving system (LS)on the basis of a detection result obtained by using the first detectingsystem (130) during detecting the positional information of the onestage (WS1) and a detection result obtained by using the seconddetecting system (132) during the exposure operation for the one stage.And, the controller may control the substrate-driving system (LS) forthe one stage by using only the detection result obtained by using thesecond detecting system (132) upon exposure for the other shot areasthan the shot areas in the vicinity of outer circumstance to perform analignment in the exposure of the shot area. In this case, when the shotareas in the vicinity of the outer circumference, which are set to besubjected to scanning from the outside to the inside of the sensitivesubstrate, concerning the exposure area for which information on thesurface position of the sensitive substrate during exposure for theprevious shot is not obtained, are exposed during the exposure operationfor the one stage, the substrate-driving system for the one stage can becontrolled on the basis of the detection result obtained by using thefirst detecting system during the mark-measuring operation for the onestage to drive the surface position of the sensitive substrate into theposition near to the image formation plane of the projection opticalsystem. Further, the substrate-driving system can be further adjustedfinely on the basis of the detection result obtained by using the seconddetecting system so that the surface of the sensitive substratecoincides with the image formation plane. On the contrary, upon exposurefor shot areas other than the above, for which information on thesurface position of the sensitive substrate during exposure for theprevious shot is obtained, the substrate-driving system for the onestage is controlled on the basis of the information on the surfaceposition of the sensitive substrate during exposure for the previousshot prior to the start of exposure for the exposure-objective shot areaso that the surface position of the sensitive substrate is quicklydriven into the position near to the image formation plane of theprojection optical system, followed by performing the adjustment for thesurface position (“focus/leveling” adjustment) of the sensitivesubstrate by using only the detection result obtained by using thesecond detecting system during exposure. Therefore, it is possible toperform quick and highly accurate focus/leveling control in any exposureof shot area.

According to the eighth aspect of the present invention, there isprovided a projection exposure method for exposing sensitive substrates(W1 or W2) with an image of a pattern formed on a mask (R) via aprojection optical system (PL), comprising the steps of:

preparing two substrate stages (WS1, WS2) which is movable independentlyon an identical two-dimensional plane while each holding a sensitivesubstrate (W1 or W2);

measuring positional information of at least one shot area on thesensitive substrate (for example, W1) held on one stage (for example,WS1) of the two stages (WS1, WS2);

exposing the sensitive substrate (W2) held on the other stage (WS2) ofthe two stages (WS1, WS2) with the image of the pattern formed on themask (R) during the period in which the measuring operation for thepositional information is performed for the one of the stages (WS1); and

exposing the sensitive substrate held on the one of the stages (WS1),after completion of the exposure operation performed for the other ofthe stages (WS2), while adjusting a surface position of the sensitivesubstrate (W1) held on the one of the stages (WS1) on the basis of themeasured positional information.

According to the exposing method, for example, in one stage, themark-measuring operation for an alignment mark of sensitive substrateand detection of positional information such as the relative positionwith respect to the predetermined reference plane of the sensitivesubstrate are performed for one stage of the two stages, during which,in parallel thereto, the sensitive substrate held on the other stage ofthe two stages is exposed with the image of the pattern on the mask.Accordingly, owing to the concurrent and parallel process of themark-measuring operation for the one stage and the exposure operationfor the other stage, it is possible to contemplate improvement inthroughput as compared with the conventional technique in which theseoperations have been performed in a sequential manner. After completionof the exposure operation for the other stage, namely after completionof the concurrent operations on the two stages, the sensitive substrateheld on the one stage is subjected to exposure. During the exposure, thesurface position of the sensitive substrate held on the one stage isadjusted using information on the surface position of the shot area ofthe sensitive substrate held on the one stage detected previously, withrespect to the predetermined reference plane. Accordingly, during theexposure operation effected for the one stage, the surface position ofthe sensitive substrate held on the one stage can be quickly driven intoa position near to the image formation plane of the projection opticalsystem on the basis of the information on the surface positionpreviously detected. Therefore, it is possible to perform quick andhighly accurate focus/leveling control.

According to the ninth aspect of the present invention, there isprovided a projection exposure apparatus for exposing a sensitivesubstrate (W1, W2) by projecting an image of a pattern formed on a mask(R) via a projection optical system (PL) onto the sensitive substrates,characterized by comprising:

a first substrate stage (WS1) on which a reference mark is formed, formoving in a two-dimensional plane while holding a sensitive substrate(W1);

a second substrate stage (WS2) on which a reference mark is formed, formoving in the same plane as for the first substrate stage (WS1)independently of the first substrate stage (WS1) while holding asensitive substrate (W2);

at least one a mark detecting system (24 a) provided apart from theprojection optical system (PL), for detecting the reference mark on thesubstrate stage (WS1, WS2) or an alignment mark-on the sensitivesubstrate (W1, W2) held on the substrate stage (WS1, WS2);

an interferometer system provided with a first length-measuring axis(BI1X) for measuring a position of the first substrate stage (WS1) in adirection of a first axis from one side in the direction of the firstaxis passing through a projection center of the projection opticalsystem (PL) and a detection center of the mark detecting system (24 a),a second length-measuring axis (BI2X) for measuring a position of thesecond substrate stage (WS2) in the direction of the first axis from theother side in the direction of the first axis, a third length-measuringaxis (BI3Y) which perpendicularly intersects the first axis at theprojection center of the projection optical system (PL), and a fourthlength-measuring axis (BI4Y) which perpendicularly intersects the firstaxis at the detection center of the mark detecting system (24 a), theinterferometer system measuring two-dimensional positions of the firstand second substrate stages (WS1 and WS2) respectively by using thelength-measuring axes (BI1X to BI4Y).

According to the projection exposure apparatus, the sensitive substratesare held on the first and second substrate stages respectively to beindependently movable on the two-dimensional plane. The mark detectingsystem such as an alignment system, which are provided apart from theprojection optical system, are used to detect the reference mark on thesubstrate stage and/or the mark on the sensitive substrate held on thesubstrate stage. The two-dimensional positions of the first and secondsubstrate stages are measured by using the first to fourthlength-measuring axes of the interferometer system respectively. As forthe length-measuring axes of the interferometer system, the firstlength-measuring axis and the second length-measuring axis are providedon one side and the other side of the first and second substrate stagesrespectively along the direction of the first axis passing through theprojection center of the projection optical system and the detectioncenter of the mark detecting system. The first length-measuring axis isused to measure the position of the first substrate stage in thedirection of the first axis, and the second length-measuring axis isused to measure the position of the second substrate stage in thedirection of the first axis. The third length-measuring axis is providedso that it perpendicularly intersects the first axis at the projectioncenter of the projection optical system. The fourth length-measuringaxis is provided so that it perpendicularly intersects the first axis atthe detection center of the mark detecting system. Accordingly, thereference marks formed on the two substrate stages can be detected byusing the mark detecting system. During the mark detection, thetwo-dimensional position of the first substrate stage is measured byusing the interferometers having the first length-measuring axis and thefourth length-measuring axis which mutually intersect perpendicularly atthe detection center of the mark detecting system, and thetwo-dimensional position of the second substrate stage is measured byusing the interferometers having the second length-measuring axis andthe fourth length-measuring axis which mutually intersectperpendicularly at the detection center of the mark detecting system.Therefore, the position of any of the stages is accurately measuredwithout any Abbe error.

On the other hand, during the exposure for the mask pattern effected bythe projection optical system, the two-dimensional position of the firstsubstrate stage is measured by using the interferometers having thefirst length-measuring axis and the third length-measuring axis whichmutually intersect perpendicularly at the projection center of theprojection optical system, and the two-dimensional position of thesecond substrate stage is measured by using the interferometers havingthe second length-measuring axis and the third length-measuring axiswhich mutually intersect perpendicularly at the projection center.Therefore, the position of any of the stages is accurately measuredwithout any Abbe error. Especially, the first length-measuring axis andthe second length-measuring axis are arranged in the positionalrelationship as described above. Accordingly, the length-measuring axisis not intercepted during the period in which the first substrate stageand the second substrate stage are moved in the direction of the firstaxis. Therefore, the two substrate stages can be moved and reciprocatedbetween the mark detecting system and the projection optical system onthe basis of the measured values obtained by using the interferometershaving these length-measuring axes. For example, the second substratestage can be located under the projection optical system during theperiod in which the first substrate stage is disposed under the markdetecting system. Accordingly, it is possible to concurrently processthe exposure operation effected by the projection optical system and theposition-detecting operation effected by the mark detecting system forthe marks on the respective substrate stages or the marks on thesensitive substrates in parallel to one another. As a result, it ispossible to improve the throughput.

The projection exposure apparatus further may be provided with acontroller (90) for controlling the first substrate stage and the secondsubstrate stage (WS1, WS2), so that a position of one stage of the firstsubstrate stage and the second substrate stage is managed based on theuse of a measured value obtained by using the third length-measuringaxis (BI3Y) of the interferometer system, while exposing the sensitivesubstrate on the one stage, during which a positional relationshipbetween an alignment mark on the sensitive substrate held on the otherstage and a reference mark (MK) on the other stage is obtained based onthe use of a detection result obtained by using the mark detectingsystem and a measured value obtained by using the fourthlength-measuring axis (BI4Y) of the interferometer system, and afterexposing the one sensitive substrate, a position of the other stage ismeasured by using the third length-measuring axis (BI3Y), while arelative positional relationship between the reference mark on the otherstage and a predetermined reference point within a projection area ofthe projection optical system is obtained.

The controller controls the operations of the two substrate stages asfollows. That is, for example, the position of the first substrate stageis managed based on the use of the measured value obtained by using thethird length-measuring axis of the interferometer system. During theperiod in which the sensitive substrate held on the first substratestage is exposed, the positional relationship between the alignment markon the sensitive substrate held on the second substrate stage and thereference mark on the second substrate stage is detected by using thedetection result obtained by the mark detecting system and the measuredvalue by using the fourth length-measuring axis of the interferometersystem. Further, the controller measures the position of the secondsubstrate stage based on the use of the measured value obtained by usingthe third length-measuring axis, while controlling the second substratestage so that it moves to a position at which a positional relationshipbetween a reference mark on the second substrate stage and apredetermined reference point within a projection area of the projectionoptical system such as the projection center to obtain the positionalrelationship thereof. That is, the controller is capable of controllingthe operations of the two stages as follows. The position of the firststage is managed without any Abbe error with respect to the sensitivesubstrate held on the first stage, based on the use of the measuredvalue obtained by using the third length-measuring axis at theprojection center of the projection optical system, while the image ofthe pattern of the mask is projected through the projection opticalsystem, during which the positional relationship between the alignmentmark on the sensitive substrate held on the second stage and thereference mark on the second stage is accurately detected without anyAbbe error based on the use of the detection result obtained by usingthe mark detecting system and the measured value obtained by using thefourth length-measuring axis at the detection center of the markdetecting system. Accordingly, it is possible to concurrently performthe exposure operation effected on the first stage and the alignmentoperation effected on the second stage as described above. Thus, it ispossible to improve the throughput.

In addition, when the operations of the both stages are completed, thecontroller measures a position of the second substrate stage based onthe use of the measured value obtained by using the thirdlength-measuring axis, while moving the second substrate stage to theposition at which the positional relationship between the predeterminedreference point within a projection area of the projection opticalsystem and the reference mark on the second substrate stage isdetectable so as to manage the position of the second substrate stage onthe base of the reference mark. Accordingly, as for the second substratestage for which the positional relationship between the reference markon the second stage and the alignment mark on the sensitive substratehas been measured (the alignment has been completed), its position canbe managed based on the use of the measured value obtained by using thethird length-measuring axis without any inconvenience, even when thefourth length-measuring axis used during the measurement of thealignment mark falls into an immeasurable state. Therefore, it ispossible to detect the positional relationship between the referencemark on the second substrate stage and the predetermined reference pointwithin the projection area of the projection optical system. Moreover,it is possible to perform the exposure while executing the positionaladjustment for the projection area of the projection optical system andthe sensitive substrate on the basis of the positional relationship, themeasurement result of the alignment, and the measured value obtained byusing the third length-measuring axis. That is, the position of thesecond substrate stage can be managed during the exposure by using theanother length-measuring axis, even when the measurement is impossibleby using the length-measuring axis which has been used to manage theposition of the second stage during the alignment. Further, it becomesunnecessary that the alignment operation of the first or the secondsubstrate stages, the movement operation from the alignment position tothe exposure position and the exposure operation are subsequentlyobserved. Therefore, it is possible to miniaturize the reflectivesurface of the stage for reflecting the interferometer beam for each ofthe length-measuring axes. Thus, it is possible to miniaturize thesubstrate stage.

In the projection exposure apparatus, the mark detecting system may bean alignment system. Also, it is desirable that the interferometer ofthe third length-measuring axes is reset when the other stage is movedto a position at which the relative positional relationship between thereference mark on the other stage and the predetermined reference pointwithin the projection area of the projection optical system. By means ofresetting the interferometer of the third length-measuring axes at thistime, the reference mark position on the other stage on the basis of thereference point within the projection area of the projection opticalsystem and the position of the alignment mark of the sensitive substrateon the other stage is managed more easily.

The projection exposure apparatus further comprises another markdetecting system (24 b) having a detection center on the first axis,disposed on a side opposite to the mark detecting system (24 a) withrespect to the projection optical system (PL), wherein theinterferometer system further provided with a fifth length-measuringaxis (BI5Y) which perpendicularly intersects the first axis at adetection center of the another mark detecting system (24 b); and thecontroller (90) may control the first and the second stage as follows.The controller manages the position of the one substrate stage based onthe use of the measured value obtained by the third length-measuringaxis (BI3Y) of the interferometer system, while exposing the sensitivesubstrate held on the one stage during which the positional relationshipbetween the alignment mark on the sensitive substrate held on the otherstage and the reference mark on the other stage is obtained based on theuse of the detection result obtained by using the mark detecting systemand the measured value obtained by using the fourth length-measuringaxis (BI4Y) of the interferometer system, and, after exposing the onestage, moving the one stage so that, the reference mark on the one stageis positioned within the another mark detecting system while theposition of the one stage is measured based on the use of the measuredvalue obtained by using the fifth length-measuring axis (BI5Y).

The controller is capable of controlling the operations of the twostages as follows. That is, the position of the first substrate stage ismanaged without any Abbe error with respect to the sensitive substrateheld on the first substrate stage, based on the use of the measuredvalue obtained by using the third length-measuring axis whichperpendicularly intersects the length-measuring axes (the firstlength-measuring axis and the second length-measuring axis) in the firstaxis direction at the projection center of the projection opticalsystem, while the image of the pattern formed on the mask is subjectedto exposure through the projection optical system, during which thepositional relationship between the alignment mark on the sensitivesubstrate held on the second substrate stage and the reference mark onthe second substrate stage is accurately detected without any Abbe errorbased on the use of the detection result obtained by using the markdetecting system and the measured value obtained by using the fourthlength-measuring axis which perpendicularly intersects thelength-measuring axes (the first length-measuring axis and the secondlength-measuring axis) in the first axis direction at the detectioncenter of the mark detecting system. Accordingly, it is impossible toconcurrently perform the exposure operation effected on the onesubstrate stage and the alignment operation effected on the secondsubstrate stage as described above.

Then, the controller controls the operation of the first substrate stageas follows. That is, when the above-mentioned operations of the bothstages are completed, the position of the first substrate stage ismeasured by the measured value obtained by using the fifthlength-measuring axis, while obtaining the relative position between thedetection center of another mark detecting system and the reference markon the first substrate stage. Accordingly, as for the first substratestage for which the exposure for the sensitive substrate has beencompleted, the position of the first substrate stage can be managedwithout any Abbe error, based on the use of the reference mark on thefirst substrate stage and the measured value obtained by using the fifthlength-measuring axis. Further, there is no inconvenience, even when thethird length-measuring axis used during the exposure falls into animmeasurable state. Therefore, the exposure operation effected on thefirst stage and the exposure operation effected on the second stage canbe easily changed by sifting the two substrate stages in the first axisdirection, thereby, the measurement of the position of the secondsubstrate stage, for which the alignment operation has been completed,is enabled based on the use of the measured value obtained by the thirdlength-measuring axis, and the measurement of the position of the firstsubstrate stage, for which the exposure operation has been completed, isenabled based on the use of the measured value obtained by the fifthlength-measuring axis.

In this aspect, the projection exposure apparatus may further comprisesa transport system (180 to 200) for receiving and transmitting thesensitive substrate (W1, W2) between the first substrate stage (WS1) andthe second substrate stage (WS2), and it is desirable that thecontroller controls the one stage so as to position the reference markthereon within the detection area of the another mark detecting system(24 b), and at the position, the substrate is received and transmittedbetween the one stage and the transport system (180 to 200). In thisconstitution, in addition to the change between the exposure operationand the alignment operation described above, the controller allows thesubstrate to be received and transmitted between the first substratestage and the transport system in the state in which the reference markon the one stage is positioned within the detection area of the anothermark detecting system using the fifth length-measuring axis of theinterferometer system. Accordingly, the measurement of the position ofthe reference mark as the operation to start the alignment and thechange of the sensitive substrate can be performed in a stationary stateof the substrate stage. In addition to the fact that the movement timerequired for the substrate stage to move from the wafer exchangeposition to the alignment start position is zero, it is possible toperform the operations concerning the time T1, the time T2, and the timeT3, for example on the side of the first substrate stage, while it ispossible to perform the operation concerning the time T4 on the side ofthe second substrate stage. Therefore, it is possible to further improvethe throughput.

In the projection exposure apparatus of the invention, the predeterminedreference point within the projection area of the projection opticalsystem (PL) may be the projection center for the image of the patternformed on the mask (R); and the projection exposure apparatus furthermay comprise a mark position-detector (142, 144) for detecting arelative positional relationship between the projection center for theimage of the pattern formed on the mask (R) and reference marks (MK1,MK2, MK3) on the stage, via the mask (R) and the projection opticalsystem. The mark position-detector may be a detector detecting the marksthrough the projection optical system, such as a reticle alignmentmicroscope.

In the projection exposure apparatus, as for the mark detecting system,at least one or more mark detecting systems may be provided apart fromthe projection optical system. However, it is also preferable that thetwo mark detecting systems (24 a, 24 b) are disposed on one side and theother side (each side) of the projection optical system (PL) in thedirection of the first axis. When the mark detecting systems arearranged in the positional relationship as described above, then thesensitive substrate on the one substrate stage may be exposed by usingthe projection optical system located at the center (exposureoperation), during which the sensitive substrate on the other substratestage may be subjected to the mark detection by using any of the markdetecting systems (alignment operation). When the exposure operation ischanged to the alignment operation, then the substrate stage for whichthe alignment operation has been completed can be moved to the positionunder the projection optical system and the other substrate stage can bemoved to the position of the mark detecting system, only by deviatingthe two substrate stages in the direction of the first axis.

In the projection exposure, it is also preferable that the projectionexposure apparatus further comprises a controller (90) for independentlycontrolling movement of the first and second substrate stages on thebasis of a result of measurement performed by the interferometer system(for example, the length-measuring axes BI1X to BI4Y) so that each ofthe first and second substrate stages (WS1 and WS2) is capable ofperforming an exposure operation effected by the projection opticalsystem (PL) and a mark-detecting operation effected by the markdetecting system (for example, 24 a). The controller independentlycontrols the movement of the first and second substrate stages on thebasis of the result of measurement performed by the interferometersystem (for example, the length-measuring axes BI1X to BI4Y) so thateach of the first and second substrate stages is capable of performingthe exposure operation effected by the projection optical system (PL)and the mark-detecting operation effected by the mark detecting system(for example, 24 a), and hence the exposure operation effected by theprojection optical system and the mark-detecting operation effected bythe mark detecting system can be reliably performed for the sensitivesubstrate disposed on any of the substrate stages.

In this arrangement, if the spacing distance between thelength-measuring axes BI3Y and BI4Y is too large, the length-measuringaxes BI3Y, BI4Y are deviated from the substrate stage when the firstsubstrate stage and the second substrate stage are moved. On the otherhand, if such a situation is avoided, the interference between the bothstages might occur. Therefore, in order to present such inconveniences,it is desirable that the controller (90) changes the thirdlength-measuring axis (BI3Y) and the fourth length measuring axis (BI4Y)of the interferometer system (for example, the length-measuring axesBI1X to BI4Y) between detection of the mark effected by the markdetecting system (for example, 24 a) and exposure effected by theprojection optical system (PL) for the first and second substrate stages(WS1 and WS2) respectively so that no inconvenience occurs even when thesubstrate stage is deviated from the length-measuring axis. In theconstitution as described above, the spacing distance between the thirdlength-measuring axis (BI3Y) and the fourth length-measuring axis (BI4Y)can be widened to avoid the interference between the both stages.Further, when the length-measuring axis BI3Y, BI4Y is deviated from thesubstrate stages during the movement of the first substrate stage andthe second substrate stage, the controler can be used to change thelength-measuring axis so that the two-dimensional position of each ofthe substrate stages is accurately measured at each of the processingpositions by using the interferometer system.

According to the tenth aspect of the present invention, there isprovided a method for exposing sensitive substrates by projecting animage of a pattern on a mask (R) via a projection optical system ontothe sensitive substrates, characterized by:

using two substrate stages (WS1, WS2) each of which is movableindependently on an identical plane while each holding a sensitivesubstrate (W1, W2);

measuring a position of one stage of the two stages by using a firstinterferometer, while exposing the sensitive substrate (W1, W2) held onthe one stage,

measuring the position of the other stage by using a secondinterferometer during exposure for the substrate held on the one stage,while measuring a positional relationship between an alignment mark onthe substrate held on the other stage and a reference mark on the otherstage,

moving the other stage to a position at which a positional relationshipbetween the reference mark on the other stage and a predeterminedreference point within a projection area of the projection opticalsystem is obtained, after completion of the exposure for the substrateon the one stage; and

performing alignment for the sensitive substrate held on the other stageand the image of the pattern on the mask, by using the firstinterferometer, on the basis of the relationship between the alignmentmark on the substrate held on the other stage and the reference mark onthe other stage, and a relationship between the reference mark on theother stage and the predetermined reference point within the projectionarea of the projection optical system.

According to the projection exposure method, for example, the exposureoperation for the sensitive substrate held on the first substrate stage,and the measurement of the positional relationship (alignment operation)between the positional alignment mark of the sensitive substrate held onthe second substrate stage and the reference mark on the stage areperformed concurrently in parallel to one another. During this process,the position of the first substrate stage is managed by the aid of thefirst interferometer, and the position of the second stage is managed bythe aid of the second interferometer. When the exposure operationeffected on the side of the first substrate stage is completed, theposition of the second stage is measurable by using the firstinterferometer which has been used to manage the position of the firstsubstrate stage, and also, the second substrate stage is moved to theposition at which the relative position between the predeterminedreference point within the projection area of the projection opticalsystem and the reference mark on the second substrate stage isdetectable. Subsequently, the positional adjustment is performed for thesensitive substrate held on the second stage and the image of thepattern formed on the mask by using the first interferometer, on thebasis of the positional relationship between the reference mark on thesecond stage and the positional alignment mark on the sensitivesubstrate held on the second stage measured previously. Thus, thesensitive substrate is exposed by projection with the image of thepattern formed on the mask.

That is, the exposure operation for the sensitive substrate held on theone substrate stage, and the alignment operation for the sensitivesubstrate held on the second stage are concurrently performed inparallel to one another. After that, the first substrate stage isretracted to a predetermined substrate exchange position, concurrentlywith which the second substrate stage is moved toward the position onwhich the position of the reference mark of the second substrate stageis detectable with respect to the predetermined reference point (forexample, the projection center of the image of the pattern formed on themask) within the projection area of the projection optical system, andthen the positional relationship between the both is detected. Further,the alignment is performed for the sensitive substrate held on thesecond substrate stage and the image of the pattern formed on the maskon the basis of the obtained detection result and the positionalrelationship between the alignment mark and the reference mark on thestage previously measured during the alignment operation, while theposition of the second stage is managed by using the firstinterferometer.

Therefore, it is possible to improve the throughput by concurrentlyperform the exposure operation for the sensitive substrate on the firstsubstrate stage and the alignment operation for the sensitive substrateon the second substrate stage. Even when the second interferometer,which has been used to manage the position of the other stage during thealignment, cannot be used for the measurement, the measurement based onthe use of the first interferometer makes it possible to manage theposition of the second substrate stage during the exposure. Thus, itbecomes unnecessary that the stage position is observed continuously bymeans of one measuring axis or one interferometer through the alignmentoperation, the movement operation from the alignment position to theexposure position and exposure operation. Therefore, it is possible tominiaturize the reflective surface of the stage for reflecting theinterferometer beam of each of the interferometers, and thereby it ispossible to miniaturize the substrate stage.

According to the eleventh aspect of the present invention, there isprovided a projection exposure apparatus for exposing a sensitivesubstrate (W1, W2) by projecting an image of a pattern formed on a mask(R) via a projection optical system (PL) onto the sensitive substrates,characterized by comprising:

a first substrate stage (WS1) which is movable on a two-dimensionalplane while holding a sensitive substrate (W1);

a second substrate stage (WS2) which is movable independently from thefirst substrate stage (WS1) on the same plane as that for the firstsubstrate stage (WS1) while holding a sensitive substrate (W2);

a transport system (180 to 200) for delivering the sensitive substratewith respect to the first and second substrate stages (WS1, WS2); and

a controller (90) for controlling operations of the both stages so thatone stage of the first (WS1) and second (WS2) substrate stages performsdelivery of the sensitive substrate with respect to the transport system(180 to 200), during which the other stage performs an exposureoperation.

According to the projection exposure apparatus, the controller controlsthe operations of the both stages so that one stage of the firstsubstrate stage and the second substrate stage performs the delivery ofthe sensitive substrate with respect to the transport system, duringwhich the other stage performs the exposure operation. Therefore, theoperation corresponding to the time T1 explained above can be processedconcurrently with the operation corresponding to the time T4. Thus, itis possible to improve the throughput as compared with the conventionalsequential process which requires the time (T1+T2+T3+T4).

It is sufficient for any of the projection exposure apparatus that theexposure is performed by using one sheet of mask. However, it is alsopreferable that the projection exposure apparatus further comprises amask stage (RST) which is capable of simultaneously carrying a pluralityof masks (R); and a driving system (30) for driving the mask stage (RST)so that any of the masks (R) is selectively set at an exposure position.According to this embodiment, for example, in order to improve theresolving power, even when the so-called double exposure method is usedto change the two masks so that overlay exposure is performed under anexposure condition appropriate for each exposure area, then the doubleexposure can be performed in a continuous manner by using the two maskson the side of the one substrate stage, during which another operationsuch as alignment can be performed on the side of the other substratestage concurrently therewith, only by allowing the two masks to becarried on the mask stage beforehand, and changing the masks and settingthe mask stage at the exposure position by using the driving system.Thus, the low throughput, which would be otherwise resulted from thedouble exposure method, can be greatly improved.

As compared with the stationary type projection exposure apparatus suchas the stepper for exposing the sensitive substrate by projection withthe pattern formed on the mask via the projection optical system in astate in which the mask and the sensitive substrate are allowed to standstill, any of the above-mentioned projection exposure apparatus is moreeffective when the projection exposure apparatus is constructed as ascanning type projection exposure apparatus in which the mask (R) iscarried on the mask stage (RST) which is movable in a predetermineddirection, wherein the projection exposure apparatus further comprises astage controller (38) for exposing the sensitive substrate (WS1, WS2) byprojection with the pattern formed on the mask, while synchronouslymoving the mask stage (RST) with respect to any one of the first andsecond substrate stages (WS1 and WS2), because of the following reason.That is, it is possible to realize highly accurate exposure owing to theaveraging effect on the image of the mask pattern in the projection areaformed by the projection optical system, and it is possible to makeexposure for a larger area by using the smaller projection opticalsystem as compared with those used for the stationary type projectionexposure apparatus.

According to the twelfth aspect of the present invention, there isprovided a projection exposure apparatus for exposing sensitivesubstrates (W1, W2) by projecting an image of a pattern formed on a mask(R) via a projection optical system (PL) onto the sensitive substrates,characterized by having:

a first substrate stage (WS1) which is movable on a two-dimensionalplane while holding a sensitive substrate (W1);

a second substrate stage (WS2) which is movable independently from thefirst substrate stage (WS1) on the same plane as that for the firstsubstrate stage (WS1) while holding a sensitive substrate (W2);

an interferometer system (for example, a length-measuring axes BI1X toBI4Y) for measuring two-dimensional positions of the first substratestage and the second substrate stage (WS1, WS2) respectively;

a storing device (91) which stores an interference condition for theinterferometer system (for example, the length-measuring axes BI1X toBI4Y) to be used when the first substrate stage and the second substratestage cause interference with each other; and

a controller (90) for controlling movement of the both stages (WS1, WS2)to cause no interference with each other while monitoring a measuredvalue obtained by the interferometer system (for example, thelength-measuring axes BI1X to BI4Y) on the basis of the interferencecondition stored in the storing device (91).

According to the projection exposure apparatus, the interferometersystem is used to measure the two-dimensional positions of the firstsubstrate stage and the second substrate stage which are independentlymovable on the two-dimensional plane while holding the sensitivesubstrates respectively, and the movement of the both stages iscontrolled by the controller to cause no interference while monitoringthe measured value obtained by using the interferometer system, on thebasis of the interference condition stored in the storing apparatusunder which the first substrate stage and the second substrate stagecause interference with each other. Therefore, even when the two stagesare independently moved to concurrently process the two operations inparallel to one another, it is possible to prevent the two stages fromcontact (interference).

The projection exposure apparatus may further comprises an alignmentsystem provided apart from the projection optical system (PL), fordetecting a reference mark on the substrate stage (WS1, WS2) or a markon the sensitive substrate (W1, W2) held on the substrate stage (WS1,WS2); and a transport system (180 to 200) for delivering the sensitivesubstrate (W1, W2) with respect to the first substrate stage and thesecond substrate stage (WS1, WS2). The controller (90) may control thetwo substrate stages (WS1, WS2) so that one stage of the substratestages (WS1 or WS2) performs at least one operation of a mark-detectingoperation performed by the alignment system and a sensitive substrate(W1, W2)-delivering operation with respect to the transport system (180to 200), while a measured value obtained by using the interferometersystem (for example, length-measuring axes BI1X to BI4Y) is monitored,on the basis of the interference condition, during which the other stage(WS2 or WS1) is subjected to an exposure operation performed by usingthe projection optical system (PL), and when the controller (90) maycontrol such that when the both stages (WS1, WS2) come to positions tocause interference with each other, the stage (WS1 or WS2) of the bothstages (WS1, WS2), which takes a longer time until completion of theoperation, is preferentially moved until the both stages (WS1, WS2) arein a positional relationship of no interference, during which the stage(WS2 or WS1), which takes a shorter time until completion of theoperation, is allowed to wait.

According to this constitution, the controller controls the bothsubstrate stages so that the one stage of the substrate stages performsat least one of the operations of the sensitive substrate-deliveringoperation and the mark-detecting operation, while monitoring themeasured value obtained by using the interferometer system, on the basisof the interference condition, during which the other substrate stage issubjected to the exposure operation, while the controller performscontrol such that when the both stages come to the positions to causeinterference with each other, the stage, which takes a longer time untilcompletion of the operation concerning the both stages, ispreferentially moved until the both stages are in the positionalrelationship of no interference, during which the stage, which takes ashorter time until completion of the operation, is allowed to wait.Therefore, even when a situation of interference occurs during theconcurrent process for the two operations while independently moving thetwo stages, the interference of the two stages can be avoided withoutdecreasing the throughput by comparing the time until completion of theoperation for the both stages, preferentially moving the one stage, andallowing the other stage to wait.

According to the thirteenth aspect of the present invention, there isprovided a projection exposure apparatus for exposing sensitivesubstrates (W1, W2) by projecting an image of a pattern formed on a mask(R) via a projection optical system (PL) onto the sensitive substrates,characterized by comprising:

a first substrate stage (WS1), on which a reference mark is formed,moving on a two-dimensional plane while holding a sensitive substrate(W1);

a second substrate stage (WS2), on which a reference mark is formed, formoving independently from the first substrate stage (WS1) on the sameplane as that for the first substrate stage (WS1) while holding asensitive substrate (W2);

an alignment system (for example, 24 a) provided apart from theprojection optical system (PL), for detecting the reference mark on thesubstrate stage (WS1 or WS2) or a mark on the sensitive substrate (W1 orW2) held on the substrate stage (WS1 or WS2); and

a controller (90) for controlling the two stages (WS1, WS2) so that amark-detecting operation is performed by the alignment system (forexample, 24 a) for the sensitive substrate held on one stage (WS1 orWS2) of the first substrate stage (WS1) and the second substrate stage(WS2), concurrently with which an exposure operation is performed forthe sensitive substrate held on the other stage (WS2 or WS1), while anoperation, which is included in the mark-detecting operation to beperformed on the one stage (WS1 or WS2) and which affects the otherstage (WS2 or WS1), is performed in synchronization with an operationwhich is included in the exposure operation to be performed on the otherstage (WS2 or WS1) and which affects the one stage (WS1 or WS2), and forcontrolling the operations of the two substrate stages (WS1, WS2) sothat operations, which are included in the respective operations to beperformed on the first substrate stage (WS1) and the second substratestage (WS2) and which make no influence with each other, are performedin synchronization with each other.

In the projection exposure apparatus, the controller controls the twostages so that the operation, which is included in the mark-detectingoperation operated on the one stage and which affects the other stage(disturbance factor), is performed in synchronization with the operationwhich is included in the exposure operation operated on the other stageand which affects the one stage (disturbance factor). Accordingly, theoperations, which make influence with each other, are synchronized.Therefore, no trouble occurs in the operations performed on therespective stages. Further, the controller controls so that theoperations, which are included in the respective operations to beperformed by the both stages and which make no influence with each other(non-disturbance factor), are performed in a synchronized manner.Therefore, no trouble occurs also in this case in the operationsperformed on the respective stages. Therefore, the position-detectingoperation performed by the alignment system for the marks on therespective substrate stages or on the sensitive substrates can beconcurrently processed in parallel to the exposure operation performedby the projection optical system. Consequently, it is possible toimproved the throughput. Further, it is possible to concurrently processthe two operations in an appropriate manner, because the operationsperformed on the two substrate stages make no influence with each other.

In this aspect, various combinations may be conceived for the operationswhich make no influence with each other. However, it is preferable thatthe one stage (WS1 or WS2) is stationarily rested to measure the mark onthe one stage (WS1 or WS2) or the mark on the sensitive substrate (W1 orW2) held on the one stage (WS1 or WS2) during a period for exposing, byprojection, the sensitive substrate (W2 or W1) held on the othersubstrate stage (WS2 or WS1) with the image of the pattern formed on themask (R). These operations do not make any influence with each other.Accordingly, it is possible to concurrently process, without anytrouble, the highly accurate mark-detecting operation and the exposureoperation.

On the other hand, various combinations may be conceived for theoperations which make influence with each other. However, it ispreferable that the one substrate stage (WS1 or WS2) is moved fordetecting the next mark in synchronization with movement of the othersubstrate stage (WS2 or WS1) for the next exposure.

In this embodiment, it is preferable that the projection exposureapparatus further comprises a mask stage (RST) which is movable in apredetermined direction while carrying the mask (R), and a scanningsystem (for example, 38) for synchronously scanning the mask stage (RST)and the first substrate stage (WS1) or the second substrate stage (WS2)with respect to the projection optical system (PL), wherein thecontroller (90) stationarily rests the one stage (WS1 or WS2) to measurethe mark on the one stage (WS1 or WS2) or the mark on the sensitivesubstrate (W1 or W2) held on the one stage (WS1 or WS2) during movementof the other substrate stage (WS2 or WS1) at a constant velocity insynchronization with the mask stage (RST). Accordingly, the scanningsystem is operated to move the mask stage and the other substrate stageat the constant velocity in a synchronized manner during the exposure.Therefore, the one stage is not affected thereby, for which themeasurement of the mark is performed. The mark is measured in astationary state which does not affect the other stage during theexposure, on the one stage for which the mark measurement is performed,during the movement of the other stage at the constant velocity (duringthe exposure). Accordingly, even during the process of the scanningexposure, the exposure operation and the mark-detecting operation can beconcurrently dealt with in parallel to one another without any troubleby using the two stages.

In this embodiment, it is more desirable that the projection exposureapparatus further comprises a transport system (180 to 200) fordelivering the sensitive substrate (W1 or W2) with respect to the firstsubstrate stage and the second substrate stage (WS1, WS2) respectively,wherein the controller (90) controls operations of the two substratestages (WS1, WS2) so that the one substrate stage (WS1 or WS2) performsat least one of the mark-detecting operation and a sensitive substrate(W1 or W2)-delivering operation with respect to the transport system(180 to 200), concurrently with which the exposure operation isperformed for the sensitive substrate (WS2 or WS1) held on the otherstage, while an operation, which is included in the delivering operationand the mark-detecting operation to be performed on the one substratestage (WS1 or WS2) and which affects the other stage (WS2 or WS1), isperformed in synchronization with the operation which is included in theexposure operation to be performed on the other stage (WS2 or WS1) andwhich affects the one stage (WS1 or WS2), and the controller (90)controls the operations of the two substrate stages (WS1, WS2) so thatthe operations, which are included in the respective operations to beperformed on the first substrate stage and the second substrate stage(WS1, WS2) and which make no influence with each other, are performed insynchronization with each other. According to this embodiment, theoperations corresponding to the time T1, the time T2, and the time T3explained above can be performed on the side of the one stage, while theoperation corresponding to the time T4 can be performed on the side ofthe other stage. Therefore, the throughput is further improved, and itis possible to concurrently process the operations on the two stagesrespectively without any trouble.

In the projection exposure apparatus, the alignment system may beprovided separately from the projection optical system. However, whenthe apparatus comprises, for example, two alignment systems separatelyfrom the projection optical system, it is preferable that the alignmentsystems (24 a, 24 b) are arranged on both sides of the projectionoptical system (PL) in a predetermined direction; and the controller(90) changes the operations of the both stages (WS1, WS2) when theoperations of the both of the first substrate stage and the secondsubstrate stage (WS1, WS2) are completed.

In the case of the above constitution, the projection optical systemdisposed at the central position is used to expose the sensitivesubstrate held on the one substrate stage (exposure operation), whilethe one alignment system is used to detect the mark for the sensitivesubstrate held on the other substrate stage (alignment operation). Whenthe exposure operation is changed to the alignment operation, only themovement of the two substrate stages toward the other alignment systemalong the predetermined direction makes it possible to move the onesubstrate stage having been located under the projection optical systemto the position for the other alignment system, and move the othersubstrate stage having been located at the position for the onealignment system to the position under the projection optical systemwith ease. Thus, the two alignment systems can be alternately used asdescribed above without any trouble.

According to the fourteenth aspect of the present invention, there isprovided a projection exposure method for exposing sensitive substrates(W1, W2) by projecting an image of a pattern formed on a mask (R) via aprojection optical system (PL) onto the sensitive substrates,characterized by comprising:

preparing two substrate stages, each of which moves independently on atwo-dimensional plane while holding a sensitive substrate (W1, W2), eachstage having a reference mark formed thereon; and

exposing, by projection, the sensitive substrate (W1 or W2) held on oneof the stages (WS1 or WS2) with the image of the pattern formed on themask, while stationarily resting the other stage (WS2 or WS1) to detectthe reference mark on the other stage (WS2 or WS1) or a mark on thesensitive substrate (W1 or W2) held on the other stage (WS2 or WS1).

According to the projection exposure apparatus, the other stage isstationarily rested during the projection exposure with the image of thepattern formed on the mask for the sensitive substrate held on the onestage of the two substrate stages to detect the reference mark on theother stage or the alignment mark on the sensitive substrate held on theother stage. Therefore, the two stages are used such that the projectionexposure operation is performed on the one stage, during which themark-detecting operation is performed on the other stage in thestationary state. Therefore, the highly accurate exposure operation andthe mark-detecting operation are concurrently dealt with in parallel toone another without being affected by the operation performed on the onestage or the other stage with each other. Thus, it is possible toimprove the throughput.

According to the fifteenth aspect of the present invention, there isprovided a projection exposure method for exposing sensitive substrates(W1, W2) by projecting an image of a pattern formed on a mask (R) via aprojection optical system (PL) onto the sensitive substrates,characterized by comprising:

preparing two substrate stages, each of which moves independently on atwo-dimensional plane while holding a sensitive substrate (W1, W2), eachstage having a reference mark formed thereon; and

successively exposing, by projection, a plurality of portions on thesensitive substrate (W1, W2) held on one stage (WS1 or WS2) of the twosubstrate stages (WS1, WS2) with the image of the pattern formed on themask (R), and successively detecting a plurality of marks on thesensitive substrate (W1, W2) held on the other stage (WS2 or WS1)concurrently therewith, while determining an order of the detection ofthe marks on the sensitive substrate (W1, W2) held on the other stage(WS2 or WS1) so that the two substrate stages (WS1, WS2) cause nointerference with each other.

According to the present invention, the projection exposure issuccessively performed with the image of the pattern formed on the maskfor the plurality of portions on the sensitive substrate held on the onestage of the two substrate stages which are independently movable on thetwo dimensional plane while holding the sensitive substratesrespectively, concurrently with which the plurality of marks on thesensitive substrate held on the other stage are successively detected.During this process, the order of the detection of the marks on thesensitive substrate held on the other stage is determined so that thetwo substrate stages cause no interference with each other. Therefore,the order of the detection of the marks is determined in conformity withthe movement of the stage which is subjected to the successiveprojection exposure process. Accordingly, the two stages are preventedfrom interference with each other, and the throughput can be improved byconcurrently processing the operations.

According to the sixteenth aspect of the present invention, there isprovided a scanning type projection exposure apparatus for exposing asensitive substrate (W) with an image of a pattern formed on a mask (R)by moving the sensitive substrate (W) in a scanning direction withrespect to an exposure area (IF) which is conjugate to an illuminationarea (IA) illuminated with an illumination light beam (EL), insynchronization with movement of the mask (R) in the scanning directionwith respect to the illumination area (IA), the projection exposureapparatus comprising:

a substrate stage (WS) which is movable on a two-dimensional plane whileholding the sensitive substrate (W);

a position-detecting system (151, 161) including detecting areas havinga width, in a non-scanning direction perpendicular to a scanningdirection, which is wider than that of an exposure area (IF), on oneside and the other side in the scanning direction with respect to theexposure area (IF), for detecting a relative position of a surface ofthe sensitive substrate (W) with respect to a predetermined referenceplane at least at one of a plurality of detecting points (for example,FA1 to FA9) set in the respective detecting areas along the non-scanningdirection;

a substrate-driving system (LS) provided on the substrate stage (WS),which adjusts a surface position of the sensitive substrate (W) held onthe stage (WS); and

a controller (90) which controls the substrate-driving system (LS) onthe basis of detection result obtained by using the position-detectingsystem (151, 161), upon exposure for the sensitive substrate (W) held onthe substrate stage (WS).

According to the projection exposure apparatus, the position-detectingsystem is arranged on each side in the scanning direction with respectto the exposure area, in the non-scanning direction perpendicular to thescanning direction respectively, having the detecting area with thewidth in the non-scanning direction wider than the exposure area. Therelative position of the surface of the sensitive substrate with respectto the predetermined reference plane is detected at least at one of theplurality of detecting points set in the respective detecting areasalong the non-scanning direction. The controller controls thesubstrate-driving system on the basis of the detection results obtainedby using the position-detecting systems, upon exposure for the sensitivesubstrate held on the substrate stage. Accordingly, for example, unlikethe conventional pre-measurement sensor merely including the detectingarea having the same width as the exposure area in which it has beendifficult to perform pre-measurement control in the area in the vicinityof the outer circumference of the sensitive substrate when the scanningis performed from the outside to the inside of the sensitive substrate,it is possible to detect the relative position of the surface of theadjacent portion of the sensitive substrate with respect to thepredetermined reference plane, owing to the detecting points of the partof the detecting area protruding to the outside of the exposure areaeven in such a case. It is possible to adjust the surface position ofthe sensitive substrate by controlling the substrate-driving system onthe basis of the detection data. Therefore, it is possible to avoiddecrease in throughput which would be otherwise caused by the change inscanning direction for the sensitive substrate. It is possible to drivethe focus control by utilizing the detection data.

Alternatively, during the exposure for a certain shot area existing atthe outer circumference portion of the substrate, the information on thesurface position of a shot area adjacent thereto is detected by usingthe detecting points at the portions of the detecting area disposed onone side and the other side in the scanning direction protruding overthe outside of the exposure area, and an obtained result is stored. Bydoing so, when the adjacent shot area is exposed, even if the adjacentshot is a shot area for which it is difficult to perform pre-measurementcontrol by using the conventional pre-measurement sensor describedabove, it is possible to quickly drive the focus on the basis of thestored information on the surface position.

In this aspect, it is preferable that the controller (90) controls thesubstrate-driving system (LS) on the basis of at least one detectionresult for the plurality of detecting points (for example, FA1 to FA9)in the detecting area set on a front side of the exposure area inrelation to the scanning direction for the sensitive substrate, of thedetection results obtained by using the position-detecting systems. Thatis, the position-detecting system may be used as only a pre-measurementsensor.

Alternatively, various opportunities can be considered as timings tostart control of the substrate-driving system in order to adjust thesurface position of the sensitive substrate. However, it is preferablethat when shot areas (212) in the vicinity of outer circumference of thesensitive substrate (W) are subjected scanning exposure from the outsideto the inside of the sensitive substrate (W), the controller (90) startscontrol for the substrate-driving system (LS) for adjusting the surfaceposition of the sensitive substrate (W) on the basis of a detectionresult for a detecting point (FAA1 to FA9) which overlaps the sensitivesubstrate (W), from a point of time at which at least one of theplurality of detecting points (for example, FA1 to FA9) overlaps aneffective area on the sensitive substrate (W), because of the followingreason. That is, it is possible to quickly move the surface into adesired position (focus onto the surface) by starting the control of thesubstrate-driving system from the state in which at least one of thedetecting points overlaps the effective area.

Alternatively, when one detecting point overlaps the shot area, thesurface position (including the inclination) of the sensitive substrateis adjusted as follows by the aid of the substrate-driving system. Thatis, it is preferable that when shot areas (212) in the vicinity of outercircumference of the sensitive substrate (W) are subjected scanningexposure, if only one detecting point (for example, FA3 to FA7) overlapsthe shot area (212), then the controller (90) adjusts an inclination ofthe sensitive substrate (W) by the aid of the substrate-driving system(LS) on the basis of a predetermined fixed value. The predeterminedfixed value is exemplified by an inclination of zero. In this case, thesurface of the sensitive substrate is set on a horizontal planeincluding the surface position in the direction perpendicular to thereference plane detected by using the detecting points. Therefore, evenwhen only one detecting point is used, it is possible to perform theleveling control in addition to the focus control.

Alternatively, it is preferable that when shot areas (212) in thevicinity of outer circumference of the sensitive substrate (W) aresubjected scanning exposure, if only one detecting point (for example,FA3 to FA7) overlaps the shot area (212), then the controller (90)adjusts an inclination of the sensitive substrate (W) by the aid of thesubstrate-driving system (LS) on the basis of a detection result for theonly one detecting point and a detection result for another detectingpoint (for example, FA1, FA2, FA8, FA9) which overlaps a shot areaadjacent to the shot area (212) overlapped by the one detecting point.As described above, even when one detecting point in the exposure shotarea is used, it is possible to perform the focus/leveling control withrelative accuracy, by using the detection result for the adjacent shotarea and the detection result for the one point. Further, it may bepreviously determined that a detection result of what detecting pointincluded in the plurality of detecting points (for example, FA1 to FA9)is used for each of the plurality of shot areas (212) on the sensitivesubstrate (W), and when a certain shot area (212) on the sensitivesubstrate (W) is subjected to scanning exposure, the controller (90)adjusts the surface position of the sensitive substrate (W) by the aidof the substrate-driving system (LS) by using only the detection resultfor the detecting point determined for the shot area (212). As describedabove, the detecting point, which is suitable to detect the surfaceposition corresponding to each of the shot areas, is previouslydetermined, and thus it is possible to adjust the surface position(perform the focus/leveling control) with good efficiency and with lesserror.

It is desirable that the effective area on the sensitive substrate isdisposed inside a prohibition zone (pattern prohibition zone) definedover an entire surface of the sensitive substrate (W) or at acircumferential edge portion of the sensitive substrate (W). In thisembodiment, from the point of time at which at least one of thedetecting points overlaps the inside of the sensitive substrate or theprohibition zone defined at the circumferential edge portion of thesensitive substrate, the control of the substrate-driving system isstarted in order to adjust the surface position of the sensitivesubstrate. Especially, the use of the inside of the prohibition zonedefined at the circumferential edge portion of the sensitive substratemakes it difficult to be affected by dust and camber existing in thevicinity of the outer circumference of the sensitive substrate.Therefore, it is possible to detect the surface position of thesensitive substrate more accurately.

Various judgement standards are conceived to make judgement whether ornot the area is the effective area. However, it is preferable that thecontroller (90) judges whether or not any detecting point (FA1 to FA9)for the position-detecting system (151, 161) overlaps the effective areaon the sensitive substrate (W), on the basis of positional informationon outer circumference of the sensitive substrate (W), positionalinformation on the respective detecting points (for example, FA1 to FA9)for the position-detecting system (151, 161), and positional informationon the shot area (212) to be subjected to exposure. Accordingly, it ispossible to accurately judge whether or not any of the detecting pointsfor the position-detecting system overlaps the effective area on thesensitive substrate. Thus, it is possible to accurately start thecontrol of the adjustment of the surface position of the sensitivesubstrate effected by the substrate-driving system.

As another judgement standard to make judgement whether or not the areais the effective area, for example, it is preferable that the controller(90) judges whether or not any of the detecting points (FA1 to FA9) forthe position-detecting system (151, 161) overlaps the effective area onthe sensitive substrate (W) by comparing a predetermined allowable valuewith the detection results for the plurality of detecting points (forexample, FA1 to FA9) for the position-detecting system (151, 161). Inthis embodiment, the effective area is judged in accordance with whetheror not the detection value is included in the range of the predeterminedallowable value. Even in the case of those included in the effectiverange, if any error factor exists due to any influence of dust or camberof the sensitive substrate, such a factor can be removed provided thatit is excluded from the range of the allowable value. Therefore, thisembodiment is advantageous in that an unexpected situation can be dealtwith.

As for the timing to start adjustment for the inclination of thesensitive substrate by the aid of the substrate-driving system by usingthe control system, for example, the following procedure is available.That is, it is preferable that when the shot area (212) in the vicinityof the outer circumference of the sensitive substrate (W) is subjectedscanning exposure, the controller (90) starts, from a point of time atwhich a plurality of detecting points (for example, FA1 to FA9) overlapthe shot area (212), adjustment for the inclination of the sensitivesubstrate (W) on the basis of only the detection results for thedetecting points (FA1 to FA9) which overlap the shot area (212), by theaid of the substrate-driving system (LS). Accordingly, when theplurality of detecting points overlap the shot area, the inclination ofthe surface of the shot area can be known. Thus, it is possible toperform the leveling control accurately.

Various judgement standards are conceived to judge whether or not anydetecting point for the position-detecting system overlaps any shotarea. However, it is preferable that the controller (90) judges whetheror not any detecting point for the position-detecting system (151, 161)overlaps the shot area (212), on the basis of positional information onouter circumference of the sensitive substrate (W), positionalinformation on the respective detecting points (for example, FA1 to FA9)for the position-detecting system (151, 161), and positional informationon the shot area (212) to be subjected to exposure. Accordingly, it ispossible to accurately judge whether or not any of the detecting pointsfor the position-detecting system overlaps any shot area on thesensitive substrate. Thus, in the inventions, it is possible toaccurately judge the number of detecting points overlapping the shotarea. Alternatively, it is preferable that when the shot area (212) inthe vicinity of the outer circumference of the sensitive substrate (W)is subjected to scanning exposure, if only one detecting point (forexample, FA1 to FA9) overlaps the shot area (212), then the controller(90) starts adjustment for the inclination of the sensitive substrate(W) by the aid of the substrate-driving system (LS) on the basis ofdetection results for a predetermined number of detecting points (FA1 toFA9) including the only one detecting point (one point included in FA1to FA9) and at least one detecting point (adjoining point included inFA1 to FA9) adjacent thereto, and then the detecting point (FA1 to FA9)to be used for the adjustment for the inclination is successivelyshifted toward the inside of the shot area (212). Even when only onedetecting point overlaps the shot area, the adjustment for theinclination of the sensitive substrate is started on the basis of thedetection results for the detecting points including at least onedetecting point adjacent to the one detecting point, and the detectingpoint to be used for the inclination adjustment is successively shiftedtoward the inside of the shot area, in accordance with the increase inthe number of detecting points disposed at the inside of the shot area.Thus, it is possible to perform the adjustment for the inclination moreaccurately.

According to the seventeenth aspect of the present invention, there isprovided a scanning exposure method for exposing a sensitive substrate(W) with an image of a pattern formed on a mask (R) by moving thesensitive substrate (W) in a scanning direction with respect to anexposure area (IF) which is conjugate to an illumination area (IA)illuminated with an illumination light beam (EL), in synchronizationwith movement of the mask (R) in the scanning direction with respect tothe illumination area (IA), the scanning exposure method comprising thesteps of:

projecting a plurality of slit images onto a surface of the sensitivesubstrate (W) in a direction inclined by a predetermined angle so thatthe plurality of slit images are arranged along a non-scanning directionin detecting areas (ABE, AFE) having a width in the non-scanningdirection perpendicular to the scanning direction wider than that of anexposure area (IF) and disposed on one side and the other side in thescanning direction with respect to the exposure area (IF), duringscanning exposure for the sensitive substrate (W);

receiving reflected light beams of the respective slit images comingfrom the sensitive substrate (W) to calculate, on the basis ofphotoelectrically converted signals thereof, relative positions on thesurface of the sensitive substrate (W) with respect to a predeterminedreference plane at respective detecting points (for example, AF1 to AF9)onto which the slit images are projected respectively; and

adjusting a surface position of the sensitive substrate (W) in theexposure area (IF) on the basis of a result of the calculation.

According to the scanning exposure method, the plurality of slit imagesare projected onto the surface of the sensitive substrate in thedirection inclined by the predetermined angle so that the plurality ofslit images are arranged along the non-scanning direction in thedetecting areas having a width, in the non-scanning directionperpendicular to the scanning direction, wider than that of the exposurearea, and disposed on one side and the other side in the scanningdirection with respect to the exposure area, during scanning exposurefor the sensitive substrate. The reflected light beams of the respectiveslit images coming from the sensitive substrate are received to obtainthe photoelectrically converted signals on the basis of which therelative positions of the surface of the sensitive substrate withrespect to the predetermined reference plane are calculated respectivelyat the respective detecting points onto which the slit images areprojected. Further, the surface position of the sensitive substrate inthe exposure area is adjusted on the basis of the result of thecalculation. Accordingly, for example, when the scanning is performedfrom the outside to the inside of the sensitive substrate upon exposurefor the area in the vicinity of the outer circumference of the sensitivesubstrate, it is possible to calculate the relative position of thesurface of the sensitive substrate with respect to the predeterminedreference plane at the detecting point on the basis of thephotoelectrically converted signal of the reflected light beam of theslit image at the detecting point protruding over the outside of theexposure area. As a result, it is possible to calculate the relativeposition of the surface of the sensitive substrate at the adjacentportion with respect to the predetermined reference plane by using thedetecting point protruding over the outside of the exposure area. It ispossible to adjust the surface position of the sensitive substrate onthe basis of the result of the calculation. Therefore, it is possible toavoid the decrease in throughput which would by otherwise caused by thechange in scanning direction for the sensitive substrate, and it ispossible to perform the focus control more accurately by utilizing thecalculated data.

According to the eighteenth aspect of the present invention, there isprovided a projection exposure method for exposing a plurality of shotareas (210) on a sensitive substrate (W1 or W2) respectively with animage of a pattern formed on a mask (R) via a projection optical system(PL) by moving the sensitive substrate (W1 or W2) in a scanningdirection with respect to an exposure area (IF) which is conjugate to anillumination area (IA) illuminated with an illumination light beam (EL),in synchronization with movement of the mask (R) in the scanningdirection with respect to the illumination area (IA), the projectionexposure method characterized by comprising the steps of:

selecting some of the plurality of shot areas (210) as sample shot areasso as to include shot areas (210) in the vicinity of outer circumferencewhich are set to be subjected to scanning from the outside to the insideof the sensitive substrate (W1 or W2) with respect to the exposure area(IF);

measuring coordinate positions of the sample shot areas respectively;

detecting a relative position of the sensitive substrate (W1 or W2) withrespect to a predetermined reference plane for each of the sample shotareas when the coordinate positions of the sample shot areas aremeasured;

determining an arrangement of the plurality of shot areas (210) on thesensitive substrate (W1 or W2) on the basis of the measured coordinatepositions of the sample shot areas;

performing positional adjustment of the respective shot areas withrespect to the image of the pattern on the mask (R) on the basis of thedetermined arrangement of the shot areas (210) while adjusting a surfaceposition of the sensitive substrate (W1 or W2) on the basis of therelative position detected by measuring the coordinate positions, whenexposure are performed for the respective shot areas (210) in thevicinity of the outer circumference which are set to be subjected toscanning from the outside to the inside of the sensitive substrate (W1or W2) with respect to the exposure area (IF).

According to the projection exposure apparatus, some of the plurality ofshot areas are selected as the sample shot areas so as to include theshot areas in the vicinity of the outer circumference which are set tobe subjected to scanning from the outside to the inside of the sensitivesubstrate with respect to the exposure area, of the plurality of shotareas on the sensitive substrate. The coordinate positions of the someof sample shot areas are measured respectively. The relative position ofthe sensitive substrate with respect to the predetermined referenceplane for each of the some of sample shot areas is detected when thecoordinate positions of the some of sample shot areas are measured.After that, the arrangement of the plurality of shot areas on thesensitive substrate is determined on the basis of the measuredcoordinate positions of the sample shot areas.

The positional adjustment with respect to the image of the pattern onthe mask is performed for the shot area on the basis of the determinedarrangement of the shot areas as described above when exposure isperformed for the respective shot areas in the vicinity of the outercircumference which are set to be subjected to scanning from the outsideto the inside of the sensitive substrate with respect to the exposurearea, and the surface position of the sensitive substrate is adjusted onthe basis of the detected relative position by measuring the coordinatepositions.

Accordingly, even in the case of exposure for the respective shot areasin the vicinity of the outer circumference which are set to be subjectedto scanning from the outside to the inside of the sensitive substratewith respect to the exposure area, it is possible to adjust the surfaceposition of the sensitive substrate on the basis of the relativeposition detected when the coordinate position is measured. Therefore,it is possible to avoid an inconvenience that the scanning direction ischanged from the inside to the outside upon exposure for such shotareas, and the throughput is sacrificed.

In this aspect, it is not necessarily indispensable that the sensitivesubstrate is moved in the same direction as that during the exposure todetect the relative position of the sensitive substrate with respect tothe predetermined reference plane, when the coordinate position of thesample shot area in the vicinity of the outer circumference is measured.However, it is desirable that the relative position of the sensitivesubstrate (W1 or W2) with respect to the predetermined reference planeis detected while moving the sensitive substrate (W1 or W2) in the samedirection as that used during exposure upon the measurement of thecoordinate positions of the shot areas (210) in the vicinity of theouter circumference which are set to be subjected to scanning from theoutside to the inside of the sensitive substrate (W1 or W2) with respectto the exposure area (IF), of the sample shot areas, because of thefollowing reason. That is, by doing so, it is possible to perform focuscontrol in which, for example, the offset, which depends on the movementdirection of the sensitive substrate (W1 or W2), is removed.

The exposure apparatus, the projection exposure apparatus and theexposure method of those aspects described above are extremely effectivefor the step and scan type projection exposure, especially suitable forperforming the double exposure in which high resolution is required inexposure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic arrangement of the projection exposureapparatus according to the first embodiment of the present invention.

FIG. 2 is a perspective view illustrating the positional relationshipamong the two wafer stages, the reticle stage, the projection opticalsystem, and the alignment systems, showing that the wafer stage WS1exists in a position information measuring section and the wafer stageWS2 exists in an exposure section.

FIG. 3 shows a plan view illustrating the arrangement of the drivingmechanism for the wafer stages.

FIG. 4 shows the AF/AL systems provided for the projection opticalsystem and the alignment systems respectively.

FIG. 5 shows a schematic arrangement of the projection exposureapparatus illustrating the layout of the AF/AL system and the TTRalignment system.

FIG. 6 shows the shape of the pattern formation plate shown in FIG. 5.

FIG. 7 shows a plan view illustrating the state in which the waferexchange/alignment sequence and the exposure sequence are executed byusing the two wafer stages.

FIG. 8 shows the state obtained after the change between the waferexchange/alignment sequence and the exposure sequence shown in FIG. 7.

FIG. 9 shows the reticle stage for the double exposure for holding thetwo reticles.

FIG. 10A shows the state in which the wafer is exposed by using thereticle having the pattern A shown in FIG. 9, and FIG. 10B shows thestate in which the wafer is exposed by using the reticle having thepattern B shown in FIG. 9.

FIG. 11 shows the order of exposure for each of the respective shotareas on the wafer held on one of the two wafer stages.

FIG. 12 shows the order of mark detection for each of the respectiveshot areas on the wafer held on the other of the two wafer stages.

FIG. 13 shows a plan view of the wafer illustrating the order ofexposure for the scanning type projection exposure apparatus, used whenall shot arrays are included in the wafer.

FIG. 14A shows a magnified plan view concerning the AF measurement forpre-measurement performed at the position A shown in FIG. 13;

FIG. 14B shows a magnified plan view concerning the AF measurement forpre-measurement performed at the position B shown in FIG. 13; and

FIG. 14C shows a magnified plan view concerning the AF measurement forpre-measurement performed at the position C shown in FIG. 13.

FIG. 15 shows a diagram illustrating the result of pre-measurementcontrol concerning Comparative Example, performed for the shot arealocated in the vicinity of the outer circumference of the wafer.

FIG. 16 shows a plan view of the wafer illustrating the order ofalignment for the scanning type projection exposure apparatus, used whenall shot arrays are included in the wafer.

FIG. 17 shows a diagram illustrating the result of pre-measurementcontrol, obtained in the first embodiment.

FIG. 18 shows a diagram illustrating the result of pre-measurementcontrol, obtained when the reproducibility in measurement involves anerror in the first embodiment.

FIG. 19A illustrates the operation for detecting the reference mark onthe fiducial mark plate based on the use of the alignment system, whichshows a situation in which the reference mark MK2 on the fiducial markplate FM1 is positioned just under the alignment system 24 a;

FIG. 19B shows an example of the shape of the reference mark MK2 and asituation of image pick-up for detecting the same by using the sensor ofthe FIA system of the alignment system 24 a; and

FIG. 19C shows a waveform signal obtained by the image processing systemwhen the image of the mark MK2 is picked up by using the sensor of theFIA system.

FIG. 20A explains the operation for measuring the mark on the fiducialmark plate based on the use of the reticle alignment microscope, whereina situation in which the reticle alignment microscope is used with theexposure light beam to detect the relative positions of the marks MK1,MK3 on the fiducial mark plate FM1 and the projected images on the wafersurface, of the marks RMK1, RMK3 on the reticle corresponding thereto;

FIG. 20B shows the projected image on the wafer, of the mark RMK on thereticle R;

FIG. 20C shows the mark MK on the fiducial mark plate;

FIG. 20D shows a situation of image pick-up performed in the systemshown in FIG. 20A, and

FIG. 20E shows the waveform signal obtained by processing the picked upimage.

FIG. 21 shows the concept of a state in which each shot on the wafer issubjected to exposure in accordance with the relative positionalrelationship between each shot and the exposure position finallycalculated.

FIG. 22 explains the operation of the second embodiment, illustrating asituation in which the interferometer having the length-measuring axisBI3Y is reset after completion of the alignment for the wafer W1 on thewafer stage WS1.

FIG. 23 explains the operation of the second embodiment, illustrating asituation in which the wafer stage WS1 is moved to the loading position,and the operation of the exposure sequence is performed on the side ofthe wafer stage WS2.

FIGS. 24A and B show a flow chart illustrating the timing controloperation which is performed when the disturbance factor operation andthe non-disturbance factor operation are performed on the two waferstages.

FIG. 25A shows a plan view of the stages illustrating thenon-interference condition which is used when the two wafer stages aremoved and controlled independently from each other, and

FIG. 25B shows a plan view of the stages illustrating the interferencecondition which is used when the two wafer stages are moved andcontrolled independently from each other.

FIG. 26 shows a flow chart illustrating the movement control operationof the two stages, which is used when the interference condition issatisfied or when the interference condition is not satisfied.

FIG. 27A shows a plan view of the wafer illustrating the sample shotsfor which the alignment is performed, and

FIG. 27B shows a plan view of the wafer illustrating the shot areas forwhich the exposure is performed.

FIG. 28A shows a plan view of the wafer illustrating the order of shotsused when the alignment sequence is performed, and

FIG. 28B shows a plan view of the wafer illustrating the order ofexposure used when the exposure sequence is performed.

FIG. 29 shows a schematic arrangement of the projection exposureapparatus according to the second embodiment.

FIG. 30 shows a perspective view illustrating the arrangement of the AFdetecting points for pre-measurement with respect to the exposure area.

FIG. 31 shows a side view of FIG. 30 as viewed in the scanningdirection.

FIG. 32 shows a plan view of FIG. 31.

FIG. 33 shows a side view of FIG. 32 as viewed in the non-scanningdirection.

FIG. 34 shows a plan view illustrating the pre-measurement controlmethod based on the use of the AF/AL system according to the secondembodiment.

FIG. 35 shows the positional relationship between the exposure area IFand the AF detecting points during the focus measurement.

FIG. 36 shows a selection procedure for designating the position of theAF detecting point used for the AF measurement for each shot area.

FIG. 37 shows the positions of the AF detecting points used when theshot area belonging to the group A is exposed, and the wafer surfaceupon the start of the pre-measurement control.

FIG. 38 shows the AF detecting points used when the focus measurement isperformed for the wafer surface by moving the AF detecting pointswithout changing the number of the AF detecting points to be used.

FIG. 39 shows the AF detecting points used when the focus measurement isperformed for the wafer surface by using all of the measurable AFdetecting points.

FIG. 40 shows the positions of the AF detecting points used when theshot area belonging to the group C is exposed, and the wafer surfaceupon the start of the pre-measurement control.

FIG. 41 shows a diagram illustrating the result of the pre-measurementcontrol performed as shown in FIG. 40.

FIG. 42 shows Comparative Example concerning the pre-measurement controlperformed when the shot array is larger than the outer circumference ofthe wafer W.

FIG. 43 shows Comparative Example concerning the pre-measurement controlperformed when the shot array is larger than the outer circumference ofthe wafer W.

FIG. 44 is a view schematically showing the entire structure of anexposure apparatus related to the fifth embodiment.

FIG. 45 is a schematic plan view of one wafer stage of FIG. 44.

FIG. 46 is a schematic plan view of the apparatus of FIG. 44.

FIG. 47 is a view showing a flow of actions in the apparatus of FIG. 44.

FIG. 48 is a schematic plan view showing the structure of a main part ofan exposure apparatus as the sixth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment]

A first embodiment of the present invention will be explained below withreference to FIGS. 1 to 18.

FIG. 1 shows a schematic arrangement of a projection exposure apparatus10 according to the first embodiment. The projection exposure apparatus10 is a projection exposure apparatus of the scanning exposure typebased on the so-called step-and-scan system. A structure and acontrolling method of the step-and-scan system projection exposureapparatus are disclosed in U.S. Pat. Nos. 5,646,413 and 5,448,332, thedisclosures of which are herein incorporated by reference.

The projection exposure apparatus 10 comprises, for example, a stageapparatus provided with wafer stages WS1, WS2 as first and secondsubstrate stages which are independently movable in the two-dimensionaldirection on a base pedestal 12 while holding wafers W1, W2 as sensitivesubstrates, a projection optical system PL disposed over the stageapparatus, a reticle-driving mechanism disposed over the projectionoptical system PL, for driving a reticle R as a mask in a predetermineddirection, i.e., in the Y axis direction in this embodiment (directionperpendicular to the plane of the paper in FIG. 1), an illuminationsystem for illuminating the reticle R from a position thereover, and acontrol system for controlling the respective components.

The stage apparatus is supported over the base pedestal 12 in a floatingmanner by the aid of an unillustrated air bearing. The stage apparatuscomprises the two wafer stages WS1, WS2 which are independently movabletwo-dimensionally in the X axis direction (lateral direction along theplane of the paper shown in FIG. 1) and in the Y axis direction(direction perpendicular to the plane of the paper shown in FIG. 1), astage-driving system for driving the wafer stages WS1, WS2, and aninterferometer system for measuring the positions of the wafer stagesWS1, WS2. As shown in FIG. 2, the wafer stage WS1 exists in thepositional information measuring section (PIS) and the wafer stage WS2exists in the exposure section(EPS), both stages WS1, WS2 can movebetween PIS and EPS, respectively.

The arrangement will be further described below. Unillustrated air pads(for example, vacuum-pre-loadable air bearings) are provided at aplurality of positions on bottom surfaces of the wafer stages WS1, WS2.The wafer stages WS1, WS2 are supported over the base pedestal 12 in afloating manner in a state in which a spacing distance of, for example,several microns is maintained in accordance with the balance between thevacuum-pre-loaded force and the air-ejecting force effected by the airpads.

As shown in a plan view in FIG. 3, two X axis linear guides (forexample, fixed magnets of a linear motor of the so-called moving coiltype) 122, 124, which extend in the X axis direction, are provided inparallel on the base pedestal 12. Two movable members 114, 118, 116,120, which are movable along the X axis linear guides respectively, areattached to the X axis linear guides 122, 124 respectively.Unillustrated driving coils are attached to bottom portions of the fourmovable members 114, 118, 116, 120 respectively so that the X axislinear guides 122, 124 are surrounded thereby at upper and lateralsides. The moving coil type linear motors for driving the respectivemovable members 114, 116, 118, 120 in the X axis direction areconstructed by the driving coils and the X axis linear guides 122, 124respectively. However, in the following description, the movable members114, 116, 118, 120 are referred to as “X axis linear motor” forconvenience.

Among them, the two X axis linear motors 114, 116 are provided at bothends of a Y axis linear guide 110 extending in the Y axis direction (forexample, a fixed coil of a linear motor of the moving magnet type)respectively. The other two X axis linear motors 118, 120 are secured toboth ends of a similar Y axis linear guide 112 extending in the Y axisdirection. Therefore, the Y axis linear guide 110 is driven along the Xaxis linear guides 122, 124 by means of the X axis linear motors 114,116, while the Y axis linear guide 112 is driven along the X axis linearguides 122, 124 by means of the X axis linear motors 118, 120.

On the other hand, an unillustrated magnet, which surrounds one of the Yaxis linear guides 110 at upper and lateral sides, is provided on thebottom of the wafer stage WS1. A moving magnet type linear motor fordriving the wafer stage WS1 in the Y axis direction is constructed bythe magnet and the Y axis linear guide 110. Further, an unillustratedmagnet, which surrounds the other Y axis linear guide 112 at upper andlateral sides, is provided on the bottom of the wafer stage WS2. Amoving magnet type linear motor for driving the wafer stage WS2 in the Yaxis direction is constructed by the magnet and the Y axis linear guide112.

That is, in the first embodiment of the present invention, thestage-driving system for two-dimensionally driving the wafer stages WS1,WS2 independently in the XY direction is constructed, for example, bythe X axis linear guides 122, 124, the X axis linear motors 114, 116,118, 120, the Y axis linear guides 110, 112, and the unillustratedmagnets disposed on the bottoms of the wafer stages WS1, WS2. Thestage-driving system is controlled by a stage control unit 38 shown inFIG. 1.

Minute yawing can be generated on the wafer stage WS1, or minute yawingcan be removed therefrom, by slightly varying the torque of the pair ofX axis linear motors 114, 116 provided at the both ends of the Y axislinear guide 110. Similarly, minute yawing can be generated on the waferstage WS2, or minute yawing can be removed therefrom, by slightlyvarying the torque of the pair of X axis linear motors 118, 120 providedat the both ends of the Y axis linear guide 112.

Wafers W1, W2 are fixed on the wafer stages WS1, WS2 by means of, forexample, vacuum suction by the aid of unillustrated wafer holders. Eachof the wafer holders is finely driven in the Z axis directionperpendicular to the XY plane and in the θ direction (rotationaldirection about the Z axis) by means of an unillustrated Z•θ drivingmechanism. Fiducial mark plates FM1, FM2, on which various fiducialmarks are formed, are placed on upper surfaces of the wafer stages WS1,WS2 to be at the substantially same height as that of the wafers W1, W2respectively. The fiducial mark plates FM1, FM2 are used, for example,when the reference position of each of the wafer stages is detected.

One side surface (left side surface in FIG. 1) 20 of the wafer stage WS1in the X axis direction, and one side surface (back side surface asviewed in the plane of the paper in FIG. 1) 21 thereof in the Y axisdirection are mirror-finished reflective surfaces. Similarly, the otherside surface (right side surface in FIG. 1) 22 of the wafer stage WS22in the X axis direction, and one side surface 23 thereof in the Y axisdirection are mirror-finished reflective surfaces. Interferometer beamsfor respective length-measuring axes (for example, BI1X, BI2X) forconstructing an interferometer system as described later on areprojected onto the reflective surfaces. Reflected light beams therefromare received by respective interferometers so as to measuredisplacements of the respective reflective surfaces from the referenceposition (in general, a fixed mirror is disposed on a side surface ofthe projection optical system or on a side surface of the alignmentoptical system, and such a position is used as the reference surface).Thus, the two-dimensional positions of the wafer stages WS1, WS2 aremeasured respectively. The construction of the length-measuring axes ofthe interferometer system will be described in detail later on.

A refractive optical system, which comprises a plurality of lenselements having a common optical axis in the Z axis direction and whichis telecentric on both sides having a predetermined reductionmagnification, for example, ⅕, is used as the projection optical systemPL. Therefore, the velocity of movement of the wafer stage in thescanning direction during scanning exposure based on the step-and-scansystem is ⅕ of the velocity of movement of the reticle stage.

As shown in FIG. 1, alignment systems 24 a, 24 b having the samefunction based on the off-axis system are installed on both sides in theX axis direction of the projection optical system PL at positionsseparated from the center of the optical axis of the projection opticalsystem PL (coincident with the projection center of the image of thereticle pattern) by an identical distance respectively. The alignmentsystems 24 a, 24 b have three types of alignment sensors based on theLSA (Laser Step Alignment) system, the FIA (Field Image Alignment)system, and LIA (Laser Interferometric Alignment) system. The alignmentsystems 24 a, 24 b make it possible to perform measurement of theposition in the X, Y two-dimensional direction of the reference mark onthe fiducial mark plate and the alignment mark on the wafer. The LSA andLIA are disclosed in U.S. Pat. No. 5,151,750 and the FIA is disclosed inU.S. Pat. No. 5,493,403, the disclosures of which are hereinincorporated by reference.

The LSA system resides in a general-purpose sensor most widely used tomeasure the mark position by irradiating the mark with a laser beam andutilizing a diffracted and scattered light beam. The LSA system has beenhitherto widely used for process wafers. The FIA system resides in asensor to measure the mark position by illuminating the mark with abroad band (wide zone) light beam such as a halogen lamp, and performingimage processing for an obtained mark image. The FIA system iseffectively used for asymmetric marks on aluminum layers and wafersurfaces. The LIA system resides in a sensor to detect positionalinformation of the mark from a phase measured by irradiating adiffraction grating-shaped mark with laser beams having slightlydifferent frequencies in two directions, and interfering two generateddiffracted light beams. The LIA system is effectively used for wafershaving small differences in level and wafers having rough surfaces.

In the first embodiment of the present invention, the three types of thealignment sensors are appropriately used depending on the purpose sothat, for example, so-called search alignment is performed for measuringthe approximate position of the wafer by detecting three points ofone-dimensional marks on the wafer, and fine alignment is performed formeasuring the accurate position of each of shot areas on the wafer.

In this embodiment, the alignment system 24 a is used, for example, tomeasure positions of the alignment marks on the wafer W1 held on thewafer stage WS1 and the reference marks formed on the fiducial markplate FM1. The alignment system 24 b is used, for example, to measurepositions of the alignment marks on the wafer W2 held on the wafer stageWS2 and the reference marks formed on the fiducial mark plate FM2.

The information, which is obtained and supplied from the respectivealignment sensors for constructing the alignment systems 24 a, 24 b, issubjected to A/D conversion by the aid of an alignment control unit 80to obtain a digital waveform signal which is computed and processed todetect the mark position. An obtained result is supplied to a maincontrol unit 90 which serves as the controller. The main control unit 90instructs the stage control unit to perform, for example, correction forthe synchronization position during the exposure depending on theobtained result.

Further, in the exposure apparatus 10 according to the first embodimentof the present invention, although not shown in FIG. 1, a pair ofreticle alignment microscopes 142, 144 are provided over the reticle Ras shown in FIG. 5. Each of the reticle alignment microscopes 142, 144comprises a TTR (Through The Reticle) alignment optical system based onthe use of an exposure wavelength for simultaneously observing thereticle mark (not shown) on the reticle R and the marks on the fiducialmark plates FM1, FM2 via the projection optical system PL. Detectionsignals obtained by using the reticle alignment microscopes 142, 144 aresupplied to the main control unit 90. In this embodiment, polarizingmirrors 146, 148 for introducing detected light beams from the reticle Rinto the reticle alignment microscopes 142, 144 respectively are movablyarranged. When the exposure sequence is started, the polarizing mirrors146, 148 are retracted by means of unillustrated mirror-driving units inaccordance with the command supplied from the main control unit 90respectively. A system equivalent to the reticle alignment microscopes142, 144 is disclosed, for example, in Japanese Laid-Open PatentPublication No. 7-176468, corresponding to U.S. Pat. No. 5,646,413 ofwhich detailed explanation will be omitted herein.

Although not shown in FIG. 1, autofocus/autoleveling measuringmechanisms (hereinafter referred to as “AF/AL system”) 130, 132, 134 forinvestigating the focusing position are provided for the projectionoptical system PL and the alignment systems 24 a, 24 b respectively asshown in FIG. 4. Among them, the AF/AL system 132 as a second detectingsystem is provided to detect whether or not the exposure surface of thewafer w coincides with (focuses with) the image plane of the projectionoptical system PL within a range of the depth of focus, because it isnecessary that the pattern formation plane on the reticle R is conjugateto the exposure surface of the wafer W in relation to the projectionoptical system PL in order to accurately transfer the pattern on thereticle R onto the wafer (W1 or W2) by means of scanning exposure. Inthe first embodiment of the present invention, a so-called multi-pointAF system is used as the AF/AL system 132. The AF/AL system is disclosedin U.S. Pat. No. 5,502,311, the disclosure of which is hereinincorporated by reference.

Now, detailed arrangement of the multi-point AF system for constructingthe AF/AL system 132 will be explained with reference to FIGS. 5 and 6.

As shown in FIG. 5, the AF/AL system (multi-point AF system) 132comprises an irradiating optical system 151 including a bundle ofoptical fibers 150, a light-collecting lens 152, a pattern formationplate 154, a lens 156, a mirror 158, and an irradiating objective lens160; and a light-collecting optical system 161 including alight-collecting objective lens 162, a rotary directional vibrationplate 164, an image-forming lens 166, and a light receiving unit 168.

The respective constitutive components of the AF/AL system (multi-pointAF system) 132 will be now explained together with their functions.

An illumination light beam having a wavelength which is different fromthat of the exposure light beam EL and at which the photoresist on thewafer W1 (or W2) is not photosensitive is introduced from anunillustrated illumination light source via the optical fiber bundle150. The illumination light beam radiated from the optical fiber bundle150 passes through the light-collecting lens 152, and the patternformation plate 154 is illuminated therewith. The illumination lightbeam transmitted through the pattern formation plate 154 passes throughthe lens 156, the mirror 158, and the irradiating objective lens 160,and the illumination light beam is projected onto the exposure surfaceof the wafer W. The image of the pattern on the pattern formation plate154 is projected obliquely with respect to the optical axis AX, and theimage is formed on the exposure surface of the wafer W1 (or W2). Theillumination light beam is reflected by the wafer W1, and it isprojected onto the light-receiving surface of the light receiving unit168 via the light-collecting objective lens 162, the rotary directionalvibration plate 164, and the image-forming lens 166. The image of thepattern on the pattern formation plate 154 is formed again on the lightreceiving surface of the light receiving unit 168. The main control unit90 is now operated to give predetermined vibration to the rotary -directional vibration plate 164 by the aid of a vibrating unit 172.Further, the main control unit 90 is operated to supply, to asignal-processing unit 170, detection signals from a large number of(specifically, the same number as that of slit patterns of the patternformation plate 154) light-receiving elements of the light-receivingunit 168. The signal-processing unit 170 performs synchronized detectionfor the respective detection signals by using the driving signal of thevibrating unit 172 to obtain a large number of focus signals which aresupplied to the main control unit 90 via the stage control unit 38.

In this embodiment, as shown in FIG. 6, a slit-shaped aperture pattern93-11 to 93-59, which comprises, for example, 5×9=45 individuals, isformed vertically on the pattern formation plate 154. The image of theslit-shaped aperture pattern is projected obliquely (at 45°) withrespect to the X axis and the Y axis, onto the exposure surface of thewafer W. As a result, as shown in FIG. 4, the slit images are formed,which are arranged in matrix, and inclined by 45° with respect to the Xaxis and the Y axis. Reference symbol IF in FIG. 4 indicates anillumination field on the wafer conjugate to the illumination area onthe reticle illuminated by the illumination system. As also clarifiedfrom FIG. 4, the detecting beam is radiated onto an area which istwo-dimensionally sufficiently larger than the illumination field IFunder the projection optical system PL.

The AF/AL systems 130, 134 as first detecting systems are constructed inthe same manner as the AF/AL system 132. That is, the first embodimentof the present invention is constructed such that approximately the samearea as that for the AF/AL system 132 used to detect the focus duringexposure can be also irradiated with the detecting beam by using theAF/AL mechanisms 130, 134 used when the alignment mark is measured.Accordingly, highly accurate alignment measurement can be performed bymeasuring the position of the alignment mark while executing theautofocus/autoleveling based on the use of the measurement and controlof the AF/AL system similar to those performed during exposure, uponmeasurement by using the alignment sensors based on the use of thealignment systems 24 a, 24 b. In other words, no offset (error) occursdue to the posture of the stage, between the process of exposure and theprocess of alignment.

Next, the reticle-driving mechanism will be explained with reference toFIGS. 1 and 2. The reticle-driving mechanism comprises a reticle stageRST which is movable in the XY two-dimensional direction over a reticlebase plate 32 while holding the reticle R, an unillustrated linear motorfor driving the reticle stage RST, and a reticle interferometer systemfor managing the position of the reticle stage RST.

The arrangement of the reticle-driving mechanism will be described infurther detail below. As shown in FIG. 2, the reticle stage RST isconstructed such that two sheets of reticles R1, R2 are placed in seriesin the scanning direction (Y axis direction). The reticle stage RST issupported in a floating manner over the reticle base plate 32 by the aidof, for example, an unillustrated air bearing. The reticle stage RST issubjected to fine driving in the X axis direction, minute rotation inthe θ direction, and scanning driving in the Y axis direction by the aidof a driving mechanism 30 (see FIG. 1) comprising, for example, anunillustrated linear motor. The driving mechanism 30 is a mechanismwhich uses a linear motor as a driving source similar to the stageapparatus described above. However, the driving mechanism -30 isindicated as a simple block in FIG. 1 for illustrative and explanatorypurposes. Accordingly, the reticles R1, R2 on the reticle stage RST areselectively used, for example, upon double exposure, in which each ofthe reticles can be subjected to scanning in synchronization with thewafer.

A parallel flat plate movement mirror 34, which is composed of the samematerial (for example, a ceramic) as that of the reticle stage RST, isprovided at an end on one side in the X axis direction on the reticlestage RST to extend in the Y axis direction. A refractive surface, whichis formed by means of mirror-finish processing, is formed on one sidesurface of the movement mirror 34 in the X axis direction. Aninterferometer beam is radiated onto the reflective surface of themovement mirror 34 from the interferometer indicated by thelength-measuring axis BI6X for constructing the interferometer system 36shown in FIG. 1. The reflected light beam is received by theinterferometer to measure the relative displacement with respect to thereference plane in the same manner as performed for the wafer stage.Thus, the position of the reticle stage RST is measured. In thisembodiment, the interferometer having the length-measuring axis BI6Xactually has two interferometer optical axes capable of performingmeasurement independently, making it possible to measure the position ofthe reticle stage in the X axis direction and measure the yawing amount.The interferometer having the length-measuring axis BI6X is used toperform synchronization control in the X direction and rotationalcontrol of the reticle stage RST in the direction to cancel the relativerotation (rotational error) between the reticle and the wafer on thebasis of the information on the X position and the information on theyawing of the wafer stages WS1, WS2 supplied from the interferometers16, 18 having length-measuring axes BI1X, BI2X disposed on the waferstage side as described later on.

On the other hand, a pair of corner cube mirrors 35, 37 are installed onthe other side (front side in the plane of the paper in FIG. 1) of thereticle stage RST in the Y axis direction as the scanning direction.Interferometer beams, which are represented by length-measuring axesBI7Y, BI8Y in FIG. 2, are radiated from a pair of unillustrateddouble-path interferometers to the corner cube mirrors 35, 37. The beamsare returned to the reflective surface of the reticle base plate 32 bythe corner cube mirrors 35, 37. The respective reflected light beamsreflected thereby return via the same optical paths, and they arereceived by the respective double-path interferometers. Thus, therelative displacements of the respective corner cube mirrors 35, 37 aremeasured with respect to the reference position (the reflective surfaceon the reticle base plate 32 as the reference position). Measured valuesobtained by the double-path interferometers are supplied to the stagecontrol unit 38 shown in FIG. 1 to obtain an average value thereof onthe basis of which the position of the reticle stage RST in the Y axisdirection is measured. The information on the position in the Y axisdirection is used for calculation of the relative position between thereticle stage RST and the wafer stage WS1 or WS2 on the basis of themeasured value obtained by the interferometer disposed on the wafer sideand having the length-measuring axis BI3Y. Further, the information isused for synchronization control between the reticle and the wafer inthe scanning direction (Y axis direction) during the scanning exposurebased thereon.

That is, in the first embodiment of the present invention, the reticleinterferometer system is constructed by the interferometer 36 and thepair of double-path interferometers represented by the length-measuringaxes BI7Y, BI8Y.

Next, an interferometer system for managing the positions of the waferstages WST1, WST2 will be explained with reference to FIGS. 1 to 3.

As shown in FIGS. 1 to 3, the interferometer beam, which is representedby the first length-measuring axis BI1X from the interferometer 16 shownin FIG. 1, is radiated onto the surface of the wafer stage WS1 on oneside in the X axis direction along the first axis (X axis) passingthrough the projection center of the projection optical system PL andthe respective detection centers of the alignment systems 24 a, 24 b.Similarly, the interferometer beam, which is represented by the secondlength-measuring axis BI2X from the interferometer 18 shown in FIG. 1,is radiated onto the surface of the wafer stage WS2 on the other side inthe X axis direction along the first axis. Reflected light beamstherefrom are received by the interferometers 16, 18 so as to measurethe relative displacements of the respective reflective surfaces fromthe reference position and measure the positions of the wafer stagesWS1, WS2 in the X axis direction. In this embodiment, as shown in FIG.2, each of the interferometers 16, 18 is a three-axis interferometerhaving three optical axes, making it possible to perform tiltmeasurement and θ measurement, in addition to the measurement for thewafer stages WS1, WS2 in the X axis direction. Output values for therespective optical axes can be independently measured. In thisembodiment, unillustrated θ stages for performing 0 rotation for thewafer stages WS1, WS2, and Z-leveling stages RS1, RS2 assubstrate-driving systems for performing minute driving and driving forinclination in the Z axis direction are actually disposed under thereflective surfaces (20-23). Accordingly, all of the driving amountsconcerning tilt control of the wafer stages can be monitored by usingthe interferometers 16, 18 (substrate-driving system).

The respective interferometer beams represented by the firstlength-measuring axis BI1X and the second length-measuring axis BI2Xalways hit the wafer stages WS1, WS2 in the all regions of the movementrange of the wafer stages WS1, WS2. Therefore, as for the X axisdirection, the positions of the wafer stages WS1, WS2 are managed on thebasis of measured values obtained by using the first length-measuringaxis BI1X and the second length-measuring axis BI2X at any time of, forexample, the exposure based on the use of the projection optical systemPL and the use of the alignment systems 24 a, 24 b.

As shown in FIGS. 2 and 3, the projection exposure apparatus is providedwith an interferometer having a third length-measuring axis BI3Yperpendicularly intersecting the first axis (X axis) at the projectioncenter of the projection optical system PL, and interferometers havinglength-measuring axes BI4Y, BI5Y respectively as fourth length-measuringaxes perpendicularly intersecting the first axis (X axis) at therespective detection centers of the alignment systems 24 a, 24 b.However, only the length-measuring axes are shown in the drawings.

In the case of the first embodiment of the present invention, themeasured values obtained by using the interferometer having thelength-measuring axis BI3Y passing through the projection center of theprojection optical system, i.e., the optical axis AX are used to measurethe positions of the wafer stages WS1, WS2 in the Y direction during theexposure based on the use of the projection optical system PL. Themeasured value obtained by using the length-measuring axis BI4Y passingthrough the detection center of the alignment system 24 a, i.e., theoptical axis SX is used to measure the position of the wafer stage WS1in the Y direction during the use of the alignment system 24 a. Themeasured value obtained by using the length-measuring axis BI5Y passingthrough the detection center of the alignment system 24 b, i.e., theoptical axis SX is used to measure the position of the wafer stage WS2in the Y direction during the use of the alignment system 24 b.

Therefore, the length-measuring axis of the interferometer in the Ydirection is deviated from the reflective surface of the wafer stageWS1, WS2 depending on the respective conditions of use. However, atleast one of the length-measuring axes, i.e., the length-measuring axesBI1X, BI2X are not deviated from the reflective surfaces of therespective wafer stages WS1, WS2. Accordingly, it is possible to resetthe interferometer on the Y side at an appropriate position at which theoptical axis of the interferometer to be used enters the reflectivesurface. The method for resetting the interferometer will be describedin detail later on.

The respective interferometers having the length-measuring axes BI3Y,BI4Y, BI5Y for Y measurement are two-axis interferometers each havingtwo optical axes. They are capable of performing tilt measurement inaddition to the measurement in the Y axis direction for the wafer stagesWS1, WS2. Output values concerning the respective optical axes can bemeasured independently.

In the first embodiment of the present invention, the interferometersystem for managing the two-dimensional coordinate positions of thewafer stages WS1, WS2 is constructed by the five interferometers intotal including the interferometers 16, 18 and the three interferometershaving the length-measuring axes BI3Y, BI4Y, BI5Y.

In the first embodiment of the present invention, the exposure sequenceis executed on one of the wafer stages WS1, WS2, while the waferexchange/wafer alignment sequence is executed on the other of the waferstages WS1, WS2 as described later on. During this process, in order notto cause any interference between the both stages, the movement of thewafer stages WS1, WS2 is managed by the stage control unit 38 inaccordance with the command given by the main control unit 90 on thebasis of the output values obtained by the respective interferometers.

Further, the main control unit 90 shown in FIG. 1 is provided with amemory 91 as a storing device in which, for example, a conditionalexpression (for example, for interference condition) is stored formanaging the movement of the wafer stages WS1, WS2.

Next, the illumination system will be explained with reference to FIG.1. As shown in FIG. 1, the illumination system comprises, for example,an exposure light source 40, a shutter 42, a mirror 44, beam expanders46, 48, a first fly's eye lens 50, a lens 52, a vibration mirror 54, alens 56, a second fly's eye lens 58, a lens 60, a fixed blind 62, amovable blind 64, and relay lenses 66, 68.

The respective components of the illumination system will now beexplained together with their functions. A laser beam is radiated fromthe light source unit 40 composed of a KrF excimer laser as a lightsource and a light-reducing system (for example, a light-reducing plate,an aperture diaphragm). The laser beam passes through the shutter 42,and then it is polarized by the mirror 44, followed by being shaped tohave an appropriate beam diameter by means of the beam expanders 46, 48.The laser beam comes into the first fly's eye lens 50. The light beamcoming into the first fly's eye lens 50 is divided into a plurality oflight beams by elements of the fly's eye lens arrangedtwo-dimensionally. The respective light beams come into the second fly'seye lens 58 again at different angles respectively by the aid of thelens 52, the vibration mirror 54, and the lens 56. The light beamoutgoing from the second fly's eye lens 58 passes through the lens 60,and it arrives at the fixed blind 62 installed at a position conjugateto the reticle R. At this position, the light beam is defined to have apredetermined cross-sectional configuration, and it passes through themovable blind 64 disposed at a position slightly de-focused from theconjugate plane of the reticle R. The light beam passes through therelay lenses 66, 68, and it is used as a uniform illumination light beamto illuminate a predetermined shape, i.e., a rectangular slit-shapedillumination area IA (see FIG. 2) on the reticle R defined by the fixedblind 62.

Next, the control system will be explained with reference to FIG. 1. Thecontrol system centers the main control unit 90, as a controller, forcontrolling and supervising the entire apparatus, and it comprises, forexample, the exposure amount control unit 70 and the stage control unit38 which are under the control of the main control unit 90.

Explanation will now be made mainly for the operations of the respectiveconstitutive components of the control system as well as the operationof the projection exposure apparatus 10 according to the firstembodiment of the present invention during the exposure.

Prior to the start of the synchronized scanning for the reticle R andthe wafer (W1 or W2), the exposure amount control unit 70 instructs ashutter-driving unit 72 to drive a shutter-driving unit 74 so that theshutter 42 is opened.

After that, the stage control unit 38 starts synchronized scanning (scancontrol) for the reticle R and the wafer (W1 or W2), i.e., the reticlestage RST and the wafer stage (WS1 or WS2) in accordance with theinstruction given by the main control unit 90. The synchronized scanningis performed by controlling the respective linear motors forconstructing the reticle-driving unit 30 and the driving system for thewafer stages by using the stage control unit 38 while monitoring themeasured values obtained by the length-measuring axis BI3Y and thelength-measuring axis BI1X or BI2X of the interferometer system and thelength-measuring axes BI7Y, BI8Y and the length-measuring axis BI6X ofthe reticle interferometer system.

At the point of time at which the both stages have been subjected toconstant velocity control within a predetermined allowable range, theexposure amount control unit 70 instructs a laser control unit 76 tostart pulse light emission. Accordingly, the rectangular illuminationarea IA on the reticle R, on which a pattern is chromium vapor-depositedon its lower surface, is illuminated with the illumination light beamemitted from the illumination system. The image of the pattern in theillumination area is reduced ⅕-fold by the aid of the projection opticalsystem PL, and it is projected for exposure onto the wafer (W1 or W2)applied with a photoresist on its surface. In this embodiment, as alsoclarified from FIG. 2, the slit width of the illumination area IA in thescanning direction is narrow as compared with the pattern area on thereticle. The image of the entire surface of the pattern is successivelyformed on the shot area on the wafer by performing synchronized scanningfor the reticle R and the wafer (W1 or W2) as described above.

Simultaneously with the start of the pulse light emission describedabove, the exposure amount control unit 70 instructs a mirror-drivingunit 78 to vibrate the vibration mirror 54 so that the vibration of thevibration mirror is continuously performed until the pattern area on thereticle R completely passes over the illumination area IA (see FIG. 2),i.e., until the image on the entire surface of the pattern is formed onthe shot area on the wafer. Thus, the non-uniformity of interferencefringe is reduced, which would be otherwise produced on account of thetwo fly's eye lenses 50, 58. The structure and the controlling method ofthe vibration mirror are disclosed in U.S. Pat. No. 5,534,970, thedisclosure of which is herein incorporated by reference.

The movable blind 64 is driven and controlled by the blind control unit39 in synchronization with the scanning for the reticle R and the waferW so that the illumination light does not leak out to the outside of theshielding area on the reticle at the shot edge portion during thescanning exposure. The series of synchronized operations are managed bythe stage control unit 38.

In relation to the pulse light emission effected by the laser controlunit 76 described above, it is necessary to emit light n times (n is apositive integer) during a period in which an arbitrary point on thewafer W1, W2 passes over the width (w) of the illumination field.Therefore, it is necessary to satisfy the following expression (1)provided that the oscillation frequency is f, and the wafer scanningvelocity is V. The control of the pulse light emission is disclosed inU.S. Pat. No. 5,591,958, the disclosure of which is herein incorporatedby reference.

f/n=V/w  (1)

Further, it is necessary to satisfy the following expression (2)provided that the radiation energy of one pulse radiated onto the waferis P, and the resist sensitivity is E.

nP=E  (2)

As described above, the exposure amount control unit 70 is constructedsuch that computing operation is performed for all variable quantitiesof the radiation energy P and the oscillation frequency f to give acommand to the laser control unit 76 so that the light-reducing systemprovided in the exposure light source 40 is controlled. Thus, theradiation energy P and the oscillation frequency f are varied, and theshutter-driving unit 72 and the mirror-driving unit 78 are controlled.

Further, for example, when correction is made for the movement startpositions (synchronization positions) of the reticle stage and the waferstage to be subjected to the synchronized scanning during the scanningexposure, the main control unit 90 instructs the stage control unit 38which controls the movement of the respective stages to make correctionfor the stage position corresponding to an amount of correction.

The projection exposure apparatus according to the first embodiment ofthe present invention further comprises a first transport system forperforming wafer exchange between itself and the wafer stage WS1, and asecond transport system for performing wafer exchange between itself andthe wafer stage WS2.

As shown in FIG. 7, the first transport system performs wafer exchangeas described later on between itself and the wafer stage WS1 disposed ata wafer loading position on the left side. The first transport systemcomprises a first wafer loader including, for example, a first loadingguide 182 which extends in the Y axis direction, first and secondsliders 186, 190 which are movable along the loading guide 182, a firstunload arm 184 which is attached to the first slider 186, and a firstload arm 188 which is attached to the second slider 190, and a firstcenter-up 180 including three vertically movable members provided on thewafer stage WS1.

The operation of wafer exchange effected by the first transport systemwill now be briefly explained. As shown in FIG. 7, explanation will bemade for a case in which the wafer W1′ placed on the wafer stage WS1disposed at the wafer loading position on the left side is exchangedwith the wafer W1 transported by the first wafer loader.

At first, the main control unit 90 is operated to turn-off vacuumattraction effected by the unillustrated wafer holder on the wafer stageWS1 by the aid of an unillustrated switch so that attraction for thewafer W1′ is de-energized.

Next, the main control unit 90 is operated to drive and raise thecenter-up 180 by a predetermined amount by the aid of an unillustratedcenter-up-driving system. Accordingly, the wafer W1′ is lifted up to apredetermined position. In this state, the main control unit 90instructs an unillustrated wafer loader control unit to move the firstunload arm 184. Accordingly, the first slider 186 is driven andcontrolled by the wafer loader control unit. The first unload arm 184 ismoved to a position over the wafer stage WS1 along the loading guide182, and it is located at the position just under the wafer W1′.

In this state, the main control unit 90 is operated to downwardly drivethe center-up 180 to a predetermined position. During the downwardmovement of the center-up 180, the wafer W1′ it is transmitted to andreceived by the first unload arm 184. Therefore, the main control unit90 instructs the wafer loader control unit to start vacuum attractionfor the first unload arm 184. Accordingly, the wafer W1′ is attractedand held by the first unload arm 184.

Next, the main control unit 90 instructs the wafer loader control unitto start retraction of the first unload arm 184 and movement of thefirst load arm 188. Accordingly, the first unload arm 184 startsmovement in the −Y direction in FIG. 7 integrally with the first slider186, simultaneously with which the second slider 190 starts movement inthe +Y direction integrally with the first load arm 188 which holds thewafer W1. When the first load arm 188 arrives at a position over thewafer stage WS1, the wafer loader control unit stops movement of thesecond slider 190, and the vacuum attraction for the first load arm 188is de-energized.

In this state, the main control unit 90 is operated to upwardly drivethe center-up 180. Thus, the underlying center-up 180 is allowed to liftup the wafer W1. Next, the main control unit 90 instructs the waferloader control unit to retract the load arm. Accordingly, the secondslider 190 starts movement in the −Y direction integrally with the firstload arm 188, and the first load arm 188 is retracted. Simultaneouslywith the start of retraction of the first load arm 188, the main controlunit 90 starts downward driving for the center-up 180. Thus, the waferW1 is placed on the unillustrated wafer holder on the wafer stage WS1,and vacuum attraction effected by the wafer holder is turned on.Accordingly, a series of sequence for wafer exchange is completed.

Similarly, as shown in FIG. 8, a second transport system performs waferexchange in the same manner as described above between itself and thewafer stage WS2 disposed at a wafer loading position on the right side.The second transport system comprises a second wafer loader including,for example, a second loading guide 192 which extends in the Y axisdirection, third and fourth sliders 196, 200 which are movable along thesecond loading guide 192, a second unload arm 194 which is attached tothe third slider 196, and a second load arm 198 which is attached to thefourth slider 200, and an unillustrated second center-up provided on thewafer stage WS2.

Next, explanation will be made with reference to FIGS. 7 and 8 for theconcurrent or parallel process based on the use of the two wafer stages,which is the feature of the first embodiment of the present invention.

FIG. 7 shows a plan view of a state in which the wafer is exchangedbetween the wafer stage WS1 and the first transport system as describedabove at the left loading position, during the period in which theexposure operation is performed for the wafer W2 on the wafer stage WS2by the aid of the projection optical system PL. In this process, afterperforming the wafer exchange, the alignment operation is continuouslyperformed on the wafer stage WS1 as described later on. In FIG. 7, theposition of the wafer stage WS2 during the exposure operation iscontrolled on the basis of measured values obtained by using thelength-measuring axes BI2X, BI3Y of the interferometer system. Theposition of the wafer stage WS1, on which the wafer exchange and thealignment operation are performed, is controlled on the basis ofmeasured values obtained by using the length-measuring axes BI1X, BI4Yof the interferometer system.

At the left loading position shown in FIG. 7, the arrangement is madesuch that the reference mark on the fiducial mark plate FM1 of the waferstage WS1 is disposed just under the alignment system 24 a (See FIG.19A). Accordingly, the main control unit 90 carries out reset for theinterferometer having the length-measuring axis BI4Y of theinterferometer system prior to the measurement of the reference mark onthe fiducial mark plate FM1, performed by using the alignment system 24a.

FIG. 19B shows an example of the reference mark MK2 and a situation ofimage pick-up for detecting the reference mark MK2 by using the sensorof the FIA system of the alignment system 24 a. In FIG. 19B, a symbol Sxindicates an image pick-up range for CCD. A cross-shaped mark indicatedby a symbol M indicates an index included in the sensor of the FIAsystem. In this drawing, only the image pick-up range in the X axisdirection is depicted. However, actually, it is a matter of course thata similar image pick-up procedure is also executed in the Y direction.

FIG. 19C shows a waveform signal obtained by using an image processingsystem included in the alignment control unit 80 when the image of themark MK2 shown in FIG. 19B is picked up by using the sensor of the FIAsystem. The alignment control unit 80 analyzes the waveform signal todetect the position of the mark MK2 on the basis of the index center.The main control unit 90 calculates the coordinate position of the markMK2 on the fiducial mark plate FM in a coordinate system (hereinafterreferred to as “first stage coordinate system”, if necessary) based onthe use of the length-measuring axes BI1X, BI4Y, on the basis of theposition of the mark MK2 and the result of measurement effected by usingthe length-measuring axes BI1X, BI4Y.

Search alignment is performed continuously after the wafer exchange andthe reset for the interferometer described above. The searchalignment,which is performed after the wafer exchange, is pre-alignmentperformed again on the wafer stage WS1, because the positional error islarge if pre-alignment is performed during only the period of transportof the wafer W1. Specifically, positions of three search alignment marks(not shown), which are formed on the wafer W1 placed on the stage WS1,are measured by using, for example, the sensor of the LSA system of thealignment system 24 a. Positional adjustment is performed for the waferW1 in the X, Y, θ directions on the basis of obtained results of themeasurement. During the search alignment, the operations of therespective components are controlled by the main control unit 90.

After completion of the search alignment, fine alignment is performed todetermine the arrangement of the respective shot areas on the wafer W1by using EGA in this embodiment. The method of EGA is disclosed in U.S.Pat. No. 4,780,617, the disclosure of which is incorporated herein byreference. Specifically, positions of the alignment marks ofpredetermined sample shots on the wafer W1 are measured by using, forexample, the sensor of the FIA system of the alignment system 24 a whilesuccessively moving the wafer stage WS1 on the basis of designed shotarray data (data on alignment mark positions), while managing theposition of the wafer stage WS1 by using the interferometer system(length-measuring axes BI1X, BI4Y). All shot array data are computed inaccordance with statistical operation based on the least square methodon the basis of obtained results of the measurement and the designedcoordinate data on the shot array. During the process of EGA, theoperations of the respective components are controlled by the maincontrol unit 90. The computing operation described above is performed bythe main control unit 90. The main control unit 90 calculates therelative positional relationship for the respective shots with respectto the mark MK2 by subtracting the coordinate position of the referencemark MK2 from the coordinate positions of the respective shots.

As described above, in the case of the first embodiment of the presentinvention, the position of the alignment mark is measured whileexecuting autofocus/autoleveling based on the measurement and controleffected by the AF/AL system 132 (see FIG. 4) in the same manner asperformed during the exposure, during the measurement performed by thealignment system 24 a. Thus, it is possible to avoid occurrence of anyoffset (error) which would be otherwise caused between the process ofalignment and the process of exposure, due to the posture of the stage.

During the period in which the wafer exchange and the alignmentoperation are performed for the wafer stage WS1 as described above,double exposure is performed for the wafer stage WS2 in a continuousmanner in accordance with the step-and-scan system while changing theexposure condition by using two reticles R1, R2 as shown in FIG. 9.

Specifically, the relative positional relationship for the respectiveshots with respect to the mark MK2 has been previously calculated in thesame manner as performed for the wafer W1. The shot areas on the waferW2 are successively positioned under the optical axis of the projectionoptical system PL, on the basis of obtained results of the calculationand results of detection of relative positions of the marks MK1, MK3 onthe fiducial mark plate FM1 and projected images on the wafer surface,of the marks RMK1, RMK3 on the reticle corresponding thereto based onthe use of the reticle alignment microscopes 144, 142 (this process willbe described in detail later on), while the reticle stage RST and thewafer stage WS2 are subjected to synchronized scanning in the scanningdirection every time when each of the shot areas is subjected toexposure. Thus, the scanning exposure is carried out.

The exposure for all of the shot areas on the wafer W2 as describedabove is also continuously performed after the reticle exchange.Specifically, the exposure procedure of the double exposure proceeds inthe following order as shown in FIG. 10A. That is, the respective shotareas on the wafer W1 are successively subjected to scanning exposurefrom A1 to A12 by using the reticle R2 (pattern A). After that, thereticle stage RST is moved in a predetermined amount in the scanningdirection by using the driving system 30 to set the reticle R1 (patternB) at the exposure position. Thereafter, scanning exposure is performedin an order from B1 to B12 as shown in FIG. 10B. In this procedure, theexposure condition (AF/AL, exposure amount) and the transmittance differbetween the reticle R2 and the reticle R1. Therefore, it is necessarythat the respective conditions are measured during the reticlealignment, and the conditions are changed depending on obtained results.The operations of the respective components during the double exposurefor the wafer W2 are also controlled by the main control unit 90.

The exposure sequence and the wafer exchange/alignment sequence areconcurrently performed in parallel on the two wafer stages WS1, WS2shown in FIG. 7 described above. In this process, the wafer stage of thetwo wafer stages WS1, WS2, on which the operation has been firstlycompleted, takes a waiting state. At the point of time at which theoperations for the both have been completed, the wafer stages WS1, WS2are controlled and moved to the positions shown in FIG. 8 respectively.The wafer W2 on the wafer stage WS2, for which the exposure sequence hasbeen completed, is subjected to wafer exchange at the right loadingposition. The wafer W1 on the wafer stage WS1, for which the alignmentsequence has been completed, is subjected to the exposure sequence underthe projection optical system PL.

At the right loading position shown in FIG. 8, the reference mark MK2 onthe fiducial mark plate FM2 is positioned under the alignment system 24b in the same manner as operated for the left loading position. Thewafer exchange operation and the alignment sequence are executed asdescribed above. Of course, the reset operation for the interferometerhaving the length-measuring axis BI5Y of the interferometer system hasbeen executed prior to the detection of the mark MK2 on the fiducialmark plate FM2 effected by the alignment system 24 b.

Next, explanation will be made for the reset operation for theinterferometer, performed by the main control unit 90 during the changefrom the state shown in FIG. 7 to the state shown in FIG. 8.

After the alignment is performed at the left loading position, the waferstage WS1 is moved to the position at which the reference mark (See FIG.20A) on the fiducial plate FM1 comes just under the center (projectioncenter) of the optical axis AX of the projection optical system PL shownin FIG. 8. During this movement, the interferometer beam for thelength-measuring axis BI4Y does not comes into the reflective surface 21of the wafer stage WS1. Therefore, it is difficult to move the waferstage to the position shown in FIG. 8 immediately after completion ofthe alignment. For this reason, in the first embodiment of the presentinvention, the following artifice is conceived.

That is, as explained above, the first embodiment of the presentinvention lies in the setting in which the fiducial mark plate FM1 comesjust under the alignment system 24 a when the wafer stage WS1 isdisposed at the left loading position. The interferometer having thelength-measuring axis BI4Y is reset at this position. Therefore, thewafer stage WS1 is once returned to this position. The wafer stage WS1is moved from the position rightwardly in the X axis direction by adistance BL while monitoring the measured value obtained by using theinterferometer 16 having the length-measuring axis BI1X for which theinterferometer beam is not intercepted, on the basis of the previouslyknown distance (conveniently referred to as “BL”) between the detectioncenter of the alignment system 24 a and the center (projection center)of the optical axis of the projection optical system PL. Accordingly,the wafer stage WS1 is moved to the position shown in FIG. 8.

As shown in FIG. 20A, the main control unit 90 is operated to detect therelative positions of the marks MK1, MK3 on the fiducial mark plate FM1and projected images on the wafer surface, of the marks RMK1, RMK3 onthe reticle corresponding thereto, based on the use of the exposurelight beam by using the reticle alignment microscopes 144, 142.

As mentioned above, the Reticle Mark RMK1 and RMK3 might generallycorrespond to or are positioned adjacent to MK1 and MK3, as shown inFIG. 20A, because the wafer stage was moved using the known value BL.

FIG. 20B shows the projected image on the wafer surface, of the mark RMK(RMK1, RMK2) on the reticle R. FIG. 20C shows the mark MK (MK1, MK3) onthe fiducial mark plate. FIG. 20D shows a situation of image pick-up forsimultaneously detecting the projected image on the wafer surface, ofthe mark RMK (RMK1, RMK2) on the reticle Rand the mark MK (MK1, MK3) onthe fiducial mark plate, by using the reticle alignment microscope 144,142, in the state shown in FIG. 20A. In FIG. 20D, a symbol SRx indicatesan image pick-up range for CCD which constructs the reticle alignmentmicroscope. FIG. 20E shows a waveform signal obtained by processing theimage picked up as described above by the aid of an unillustrated imageprocessing system.

The shapes of the reticle mark RMK shown in FIG. 20B and the mark MKshown in FIG. 20C are only examples and they may be in any shape. Asshown in FIG. 21, MK2 is arranged so as to be positioned in the mid ofMK1 and MK3 on the fiducial plate FM, and a distance between MK1 and MK3is adjusted so as to correspond to a distance between the mark RMKL andthe mark RMK2 when these marks are observed by the reticle alignmentmicroscope. FIG. 20D shows a state in which the reticle alignment markRMK is just positioned in the center of the mark MK of the fiducialplate.

The main control unit 90 resets the interferometer having thelength-measuring axis BI3Y prior to the pick-up of the waveform signal.The reset operation can be executed at the point of time at which thelength-measuring axis to be used next is available to radiate the sidesurface of the wafer stage.

Accordingly, the coordinate positions of the marks MK1, MK3 on thefiducial mark plate FM1, and the coordinate positions of the marks RMKon the reticle R projected on the wafer surface are detected in thecoordinate system (second stage coordinate system) based on the use ofthe length-measuring axes BI1X, BI3Y.

For example, when the mark MK1 (and the mark MK3) are observed by thealignment microscope, the measured value of the wafer stage WS1 in thesecond stage coordinate system is (X1, Y1), and the relative position ofmark MK1 to the position of the reticle alignment mark RMK1 and therelative position of mark MK1 to a projected position of reticlealignment mark RMK3 are detected by the alignment microscope. Here, thecenter position of the two images obtained by projecting the mark RMK1and RMK3 on the reticle R means the exposure position of the reciclepattern, i.e. the projection center of the projection optical system.Further, MK2 is positioned in the middle of the mark MK1 and MK3.Therefore, relative positions of the exposure position of the reticlepattern and the mark MK2 of the substrate plate FM can be determined bycalculation, when the wafer stage WS1 is on (X1, Y1).

The main control unit 90 finally calculates the relative positionalrelationship between the exposure position and each of the shots inaccordance with the previously determined relative positionalrelationship of each of the shots with respect to the mark MK2 on thefiducial mark plate FM1, and the relative relationship between theexposure position and the coordinate position of the mark MK1, MK3 onthe fiducial mark plate FM1. Depending on an obtained result, therespective shots on the wafer W1 are subjected to the exposure as shownin FIG. 21.

The reason why the highly accurate alignment can be performed even whenthe reset operation is performed for the interferometer as describedabove is as follows. That is, the spacing distance between the referencemark and the imaginary position calculated in accordance with themeasurement of the wafer mark is calculated by using the identicalsensor by measuring the reference mark on the fiducial mark plate FM1 bymeans of the alignment system 24 a, and then measuring the alignmentmark on each of the shot areas on the wafer W1. At this point of time,the relative distance between the reference mark and the position to besubjected to exposure is determined. Accordingly, if the correspondencebetween the exposure position and the reference mark position isestablished before the exposure by using the reticle alignmentmicroscopes 142, 144, it is possible to perform the highly accurateexposure operation by adding the relative distance to the obtainedvalue, even when the interferometer beam for the interferometer in the Yaxis direction is intercepted during the movement of the wafer stage,and the reset is performed again.

The reference marks MK1 to MK3 always exist on the identical fiducialplate. Therefore, if the drawing error is determined beforehand, onlythe management for the offset is required, and there is no variablefactor. There is a possibility that the RMK1, RMK2 also involve anyoffset due to any drawing error of the reticle. However, such asituation may be also dealt with by means of only the offset management,if the drawing error is reduced by using a plurality of marks during thereticle alignment, or if the drawing error of the reticle mark ismeasured beforehand, as disclosed, for example, in Japanese Laid-OpenPatent Publication No. 5-67271.

When the length-measuring axis BI4Y is not intercepted during the periodof movement of the wafer stage WS1 from the alignment completionposition to the position shown in FIG. 8, it is a matter of course thatthe wafer stage may be linearly moved to the position shown in FIG. 8immediately after completion of the alignment while monitoring themeasured values obtained by using the length-measuring axes BI1X, BI4Y.In this case, it is preferable to perform the reset operation for theinterferometer at any point of time at or after the point of time atwhich the length-measuring axis BI3Y passing through the optical axis AXof the projection optical system PL overlaps the reflective surface 21of the wafer stage WS1 perpendicular to the Y axis, and before thedetection of the relative positions of the marks MK1, MK3 on thefiducial mark plate FM1 and the projected images on the wafer, of themarks RMK1, RMK3 on the reticle corresponding thereto based on the useof the reticle alignment microscopes 144, 142.

The wafer stage WS2 may be moved from the exposure completion positionto the right loading position shown in FIG. 8 in the same manner asdescribed above to perform the reset operation for the interferometerhaving the length-measuring axis BI5Y.

Alternatively, FIG. 11 shows an example of the timing of the exposuresequence for successively exposing the respective shot areas on thewafer W1 held on the wafer stage WS1. FIG. 12 shows the timing of thealignment sequence for the wafer W2 held on the wafer stage WS2,performed concurrently in parallel thereto. In the first embodiment ofthe present invention, the exposure sequence and the waferexchange/alignment sequence are concurrently performed in parallel toone another for the wafers W1, W2 held on the respective wafer stageswhile independently moving the two wafer stages WS1, WS2 in thetwo-dimensional direction so that the throughput is improved.

However, when the two operations are dealt with concurrently in parallelto one another by using the two wafer stages, the operation performed onone of the stages affects, as a disturbance factor, the operationperformed on the other wafer stage in some cases. On the contrary, someof the operations performed on one of the wafer stages do not affect theoperations performed on the other wafer stage. Thus, in the firstembodiment of the present invention, the operations performedconcurrently in parallel are divided into the operations whichcorrespond to the disturbance factor, and the operations which do notcorrespond to the disturbance factor. Further, the timings of therespective operations are adjusted so that the operations whichcorrespond to the disturbance factor are mutually performedsimultaneously, or the operations which do not correspond to thedisturbance factor are mutually performed simultaneously.

For example, during the scanning exposure, the synchronized scanning forthe wafer W1 and the reticle R is performed at constant velocities, inwhich no disturbance factor is included. Further, it is necessary toexclude any external disturbance factor as less as possible. Therefore,during the scanning exposure performed on one of the wafer stages WS1,the timing is adjusted to give a stationary state in the alignmentsequence effected for the wafer W2 on the other wafer stage WS2. Thatis, the measurement of the mark in the alignment sequence is performedin a state in which the wafer stage WS2 is allowed to stand still at themark position. Therefore, the measurement of the mark is not thedisturbance factor for the scanning exposure. Thus, it is possible toperform the measurement of the mark concurrently with the scanningexposure in parallel. In this context, with reference to FIGS. 11 and12, it is understood that the scanning exposure effected for the waferW1 indicated by the operation numbers of “1, 3, 5, 7, 9, 11, 13, 15, 17,19, 21, 23” shown in FIG. 11 is performed in a mutually synchronizedmanner with respect to the mark measurement operation effected at therespective alignment mark positions for the wafer W2 indicated by theoperation numbers of “1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23” shownin FIG. 12. On the other hand, in the case of the alignment sequence,the constant velocity movement is also performed during the scanningexposure. Therefore, no disturbance occurs, and it is possible toperform the measurement highly accurately.

The same situation as that described above is also considered for thewafer exchange. Especially, for example, any vibration, which isgenerated when the wafer is transmitted from the load arm to thecenter-up, may serve as a disturbance factor. Therefore, the wafer maybe transmitted in conformity with acceleration or deceleration (whichmay serve as a disturbance factor) before or after the synchronizedscanning is performed at a constant velocity. The timing adjustmentdescribed above is performed by using the main control unit 90.

Next, explanation will be made for the method for performing thefocus/leveling control during the exposure. In the projection exposureapparatus 10 according to the first embodiment of the present invention,AF measurement is performed for the wafer during the alignment by usingthe AF/AL system 130 provided for the alignment system 24 a, or by usingthe AF/AL system 134 provided for the alignment system 24 b. Thefocus/leveling control is performed during the exposure on the basis ofobtained results of the measurement described above and results of AFmeasurement for the wafer by using the AF/AL system 132 provided for theprojection optical system PL.

As described above, the order of exposure for the respective shot areason the wafer W is determined, for example, by respective parameters of(1) to (4), i.e., (1) acceleration and deceleration times duringscanning, (2) adjustment time, (3) exposure time, and (4) stepping timeto adjacent shot. However, in general, the acceleration and thedeceleration give the rate-determining condition. Therefore, it is mostefficient that scanning is performed in an alternate manner for thewafer in the ±Y direction (the adjacent shots are successively subjectedto scanning exposure in the X direction shown in FIG. 13), when thetwo-shot stepping effected by the vertical stepping (stepping in the Ydirection shown in FIG. 13) is not performed.

FIG. 13 shows the order of exposure for the shot area 210 on the waferW1, determined as described above. FIG. 13 represents an example inwhich all shot arrays are included in the wafer W1.

The complete pre-measurement control as described in Japanese Laid-OpenPatent Publication No. 6-283403 corresponding to U.S. Pat. No. 5,448,332is also performed in the embodiment of the present invention prior tothe exposure for the respective shot areas. However, when it is intendedto perform the exposure in the most efficient exposure order as shown inFIG. 13, AF detecting points appear in some parts, at which it isimpossible to perform the measurement (detection) for the surface of thewafer W1, because the AF detecting points for pre-measurement overlapthe outer circumference of the wafer W1 at respective positionsindicated by symbols A, B, C in FIG. 13. In such a case, it isimpossible to perform the complete pre-measurement control describedabove.

This situation will be described in further detail below. FIGS. 14A, B,C show magnified plan views respectively illustrating cases in which theAF measurement for pre-measurement is performed at the respectivepositions shown by the symbols A, B, C in FIG. 13. Actually, forexample, the AF detecting points AF1 to AF5 and the exposure area IFconjugate to the illumination area IA on the reticle are fixed, withrespect to which the wafer W1 is scanned. However, for convenience,FIGS. 14A, B, C are illustrated such that the exposure area IF and theAF detecting points are scanned with respect to the wafer surface.Therefore, in the following description, explanation will be madeassuming that the direction opposite to the actual scanning directionfor the wafer W1 is the scanning direction.

In this embodiment, it is assumed that the AF detecting points AF1 toAF5 as the second detecting system are arranged in the non-scanningdirection (lateral direction in the plane of the paper) on one side ofthe exposure area IF in the scanning direction (vertical direction inthe plane of the paper) (see FIG. 14A. Further, it is assumed that theAF detecting points AB1 to AB5 as the second detecting system arearranged in the non-scanning direction on the other side of the exposurearea IF in the scanning direction (see FIG. 14B).

In FIG. 14A, when the AF measurement is performed while conductingscanning in the +Y direction, the pre-measurement control cannot beperformed, because the detecting points AF1 and AF2 are deviated fromthe surface of the wafer W1. In the case of FIGS. 14B and C, thepre-measurement control cannot be also performed, because the detectingpoints (AB1 to AB5, AF4 and AF5) are deviated from the surface of thewafer W1.

In such a situation, the scanning direction has been hitherto invertedso that the scanning (referred to as “internal scanning”) is performedfrom the inside to the outside of the wafer W1 in order that thedetecting points are not deviated from the surface of the wafer W1 atthe positions of A, B, C described above. However, if the scanningdirection is inverted, an inconvenience arises in that the exposureorder determined as described above is changed, and consequently thethroughput is decreased.

Now, an example of output results (as Z directional position on thesurface of the wafer) of an AF system in the state in which the outeredge of the wafer being moved by means of the wafer stage WS is withinthe detecting portion of the AF system is shown. As shown in FIG. 15(Comparative Example), in order to avoid the decrease in throughput asdescribed above, it is assumed that a method is adopted, in which the AFmeasurement is started at a point of time D at which the measurement canbe performed while all of the AF detecting points (for example AF1 toAF5) for pre-measurement are located on the surface of the wafer, sothat the autofocus/autoleveling control (hereinafter referred to as“AF/AL control”) is carried out. However, in the case of this method, anerror occurs in a region between Point E and Point F which represent thecompletion of follow-up control, due to delay in phase of AF/ALfollow-up. Point E in FIG. 15 indicates the position of completion offollow-up obtained when normal pre-measurement control is performed. Asclarified from FIG. 15, it is understood that such AF measurementdeteriorates the AF/AL control accuracy.

In consideration of the fact described above, in the first embodiment ofthe present invention, the AF measurement for the wafer W1 is performedduring the alignment prior to the pre-measurement during the waferexposure, under the same condition as that used in the exposure, byusing the AF/AL system 130 provided for the alignment system 24 a or byusing the AF/AL system 134 provided for the alignment system 24 b. Thus,it is intended to avoid deterioration of the AF/AL control accuracy asthe error caused by the delay in phase of follow-up control of AF/ALdescribed above. The AF/AL system 130 or the AF/AL system 134 isprovided with the AF detecting points (corresponding to AF1 to AF5, seeFIG. 14A) and the AF detecting points (corresponding to AB1 to AB5, seeFIG. 14B) as the first detecting system capable of executing the AF/ALmeasurement for the surface of the wafer W1 under the same condition asthat provided for the projection optical system PL described above.

That is, as shown in FIG. 16, the wafer W1, which is subjected to thealignment, includes a number of measuring points for EGA, i.e., AL1 toAL6 (six points). In this range, the AF measurement is performed at themeasuring points C, A, B in the same direction as that for the exposuresequence. Also in this case, in order to avoid any mutual influence onthe operations of the two substrate stages, the stepping operations(operations corresponding to the disturbance factor) are synchronizedwith each other, or the exposure operation and the alignment operation(operations not corresponding to the disturbance factor) aresynchronized with each other, and the stages are moved in an order sothat they cause no mutual interference. In this procedure, it is assumedthat there is given “exposure time>alignment time+pre-measurement time”.

FIG. 17 shows results of measurement at Point A in FIG. 16 for thedetecting points AF1 to AF5, obtained by the AF measurement during thealignment which is the feature of the present invention. In FIG. 17, forthe purpose of simplified illustration, the wafer surface position isdepicted as having the leveling of zero. However, the results for AF1 toAF5 are dispersed in ordinary cases.

In this embodiment, as shown in FIG. 14A, the AF measurement can benormally performed at the detecting points AF4 and AF5. Therefore, theobtained values of the AF measurement also indicate the wafer surfaceposition in FIG. 17. On the contrary, the detecting points AF3, AF2, AF1gradually indicate the wafer surface position in accordance with themovement in the scanning direction. When the focus measurement for theshot areas in the vicinity of the outer circumference of the wafer isperformed beforehand as described above, it is possible to know whatmeasured values are given in the following exposure sequence, forexample, at the respective positions of A, B, C in FIG. 16. Accordingly,upon the actual pre-measurement control during the exposure, theposition of the wafer is allowed to approach the target position (0)within a range of error concerning reproducibility of the measurementfor the wafer surface position as shown in FIG. 18, as compared with theprocedure shown in FIG. 15. That is, it is possible to perform quickdriving for the focus.

Originally, as described in Japanese Laid-Open Patent Publication No.6-283403, the follow-up control response in the autofocus lies in acondition under which an amount of 30% of the absolute error can befollowed as estimated as primary response. The follow-up completionpoint F appears earlier (because of an identical allowable value) bydecreasing the initial absolute value error. It is possible to completethe follow-up earlier than at the follow-up completion point E which isgiven when the normal pre-measurement control is performed.

As explained above, according to the projection exposure apparatus 10concerning the first embodiment of the present invention, the two stagesfor holding the wafers are independently moved, and the wafer exchangeand alignment operation is performed on one of the stages, while theexposure operation is concurrently performed in parallel on the otherstage. The AF measurement for the wafer surface is performed by usingthe AF/AL system of the alignment system during the alignment. At thepoint of time at which the both operations are completed, the operationsare mutually changed with each other. Therefore, the focus can bequickly driven even for shot areas which are located in the vicinity ofthe outer circumference of the wafer where the wafer surface is notdisposed at the pre-measurement position during the exposure and forwhich the scanning exposure is performed from the outside to the insideof the wafer, by previously carrying out the focus measurement at theouter circumference of the wafer and using results obtained by themeasurement. Thus, it is possible to avoid any delay in follow-up in thepre-measurement control. Therefore, the focus/leveling control can beperformed highly accurately. It is unnecessary to adopt the internalscanning even when the shot areas in the vicinity of the outercircumference of the wafer are subjected to scanning exposure from theoutside to the inside of the wafer. The respective shot areas can beexposed in the most efficient exposure order. Accordingly, it ispossible to improve the throughput.

The AF measurement during the alignment is performed while conductingthe scanning in the same direction as that for the scanning exposure forthe shot areas located at the outer circumference of the wafer.Therefore, it is possible to perform the focus control which is freefrom, for example, the offset depending on, for example, the movementdirection of the stage.

According to the projection exposure apparatus 10 concerning the firstembodiment, there are provided the two wafer stages for independentlyholding the two wafers respectively. The two wafer stages areindependently moved in the XYZ directions, wherein the wafer exchangeoperation and the alignment operation are executed for one of the waferstages, during which the exposure operation is executed for the otherwafer stage. The operations of the both are mutually changed at thepoint of time at which the both operations are completed. Accordingly,it is possible to greatly improve the throughput.

During the change of the operations described above, the interferometerhaving the length-measuring axis to be used for the operation after thechange is reset, simultaneously with which the measurement sequence isalso performed for the fiducial mark plate disposed on the wafer stage.Therefore, no special inconvenience occurs even when thelength-measuring axis of the interferometer system is deviated from thereflective surface of the wafer stage (or from the movement mirror, ifthe movement mirror is separately provided). It is possible to shortenthe reflective surface of the wafer stage (or the movement mirror, ifthe movement mirror is separately provided). Accordingly, it is possibleto easily realize miniaturization of the wafer stage. Specifically, thelength of one side of the wafer stage can be miniaturized to have a sizeof a degree which is slightly larger than the diameter of the wafer.Thus, it is possible to easily incorporate, into the apparatus, the twowafer stages which are independently movable. In addition, it ispossible to improve the positioning performance for the respective waferstages.

As for the wafer stage for which the exposure operation is performed,the mark on the fiducial mark plate is measured simultaneously with thereset for the length-measuring interferometer by using the reticlealignment microscope 142, 144 (alignment sensor based on the use of theexposure light beam) by the aid of the projection optical system PL. Asfor the wafer stage for which the wafer exchange/alignment operation isperformed, the mark on the fiducial mark plate is measuredsimultaneously with the reset for the length-measuring interferometer byusing the alignment system 24 a or 24 b (off-axis alignment sensor).Therefore, it is also possible to change the length-measuring axis ofthe interferometer for managing the position of the wafer stage duringthe alignment effected by each of the alignment systems and during theexposure effected by the projection optical system. In this process, thefollowing procedure is adopted. That is, (1) when the mark on thefiducial mark plate is measured by using the alignment system 24 a or 24b, the coordinate position of the mark is measured on the first stagecoordinate system, (2) the alignment mark of a sample shot on the waferis thereafter detected to determine the array coordinate (coordinateposition for the exposure) of each shot is determined on the first stagecoordinate system in accordance with the EGA operation, (3) the relativepositional relationship between the mark on the fiducial mark plate andthe coordinate position for the exposure of each shot is determined fromthe results obtained in (1) and (2) described above, (4) the relativepositional relationship between the mark on the fiducial mark plate andthe coordinate position of those projected from the reticle is detectedbefore the exposure on the second stage coordinate system by the aid ofthe projection optical system PL by using the reticle alignmentmicroscope 142, 144, and the exposure is performed for each shot byusing (3) and (4) described above. Accordingly, the exposure can beperformed highly accurately even in the case of the change of thelength-measuring axis of the interferometer for managing the position ofthe wafer stage. As a result, it is possible to perform the positionaladjustment for the wafer without performing the baseline measurementwhich has been hitherto carried out to measure the spacing distancebetween the projection center of the projection optical system and thedetection center of the alignment system. It is also unnecessary tocarry a large fiducial mark plate as described in Japanese Laid-OpenPatent Publication No. 7-176468.

According to the first embodiment of the present invention, there areprovided at least two alignment systems for detecting the mark, the twoalignment systems being disposed with the projection optical system PLinterposed therebetween. Accordingly, the alignment operation and theexposure operation, which are performed by alternately using therespective alignment systems, can be concurrently dealt with in parallelto one another by alternately moving the two wafer stages.

According to the first embodiment of the present invention, the waferloader for exchanging the wafer is arranged in the vicinity of thealignment system, especially to perform the operation at the respectivealignment positions. Accordingly, the change from the wafer exchange tothe alignment sequence is smoothly performed. Thus, it is possible toobtain a higher throughput.

According to the first embodiment of the present invention, theinfluence to cause deterioration of throughput disappears almostcompletely, even when the off-axis alignment system is installed at aposition greatly separated from the projection optical system PL,because the high throughput is obtained as described above. Therefore,it is possible to design and install a straight cylinder type opticalsystem having a high N.A. (numerical aperture) and having a smallaberration.

According to the first embodiment of the present invention, each of theoptical systems has the interferometer beam radiated from theinterferometer for measuring the approximate center of each of theoptical axes of the two alignment systems and the projection opticalsystem PL. Accordingly, the positions of the two wafer stages can beaccurately measured in a state free from any Abbe error at any time ofthe alignment and the pattern exposure by the aid of the projectionoptical system. Thus, it is possible to independently move the two waferstages.

The length-measuring axes BI1X, BI2X, which are provided toward theprojection center of the projection optical system PL from the bothsides in the direction (X axis direction in this embodiment) along whichthe two wafer stages WS1, WS2 are aligned, are always used to effectradiation to the wafer stages WS1, WS2 so that the positions of therespective stages in the X axis direction are measured. Therefore, it ispossible to move and control the two stages so that they exert nointerference with each other.

The interferometers are arranged so that the length-measuring axes BI3Y,BI4Y, BI5Y effect radiation in the direction (Y axis direction in thisembodiment) intersecting perpendicularly toward the positions of thedetection center of the alignment system and the projection center ofthe projection optical system PL with respect to the length-measuringaxes BI1X, BI2X. The position of the wafer stage can be accuratelycontrolled by resetting the interferometers even when thelength-measuring axis is deviated from the reflective surface due tomovement of the wafer stage.

The fiducial mark plates FM1, FM2 are provided on the two wafer stagesWS1, WS2 respectively. The positional adjustment for the wafer can beperformed by adding the spacing distance from the correction coordinatesystem obtained by previously measuring the mark position on thefiducial mark plate and the mark position on the wafer by using thealignment system, to the measured position of the fiducial plate beforethe exposure, without performing the baseline measurement for measuringthe spacing distance between the projection optical system and thealignment system as performed in the conventional technique. It isunnecessary to carry a large fiducial mark plate as described inJapanese Laid-Open Patent Publication No. 7-176468.

According to the first embodiment of the present invention, the doubleexposure is performed by using a plurality of reticles R. Accordingly,an effect is obtained to increase the resolution and improve DOF (depthof focus). However, in the double exposure method, it is necessary torepeat the exposure step at least twice. For this reason, in general,the exposure time is prolonged, and the throughput is greatly decreased.However, the use of the projection exposure apparatus according to thefirst embodiment of the present invention makes it possible to greatlyimprove the throughput. Therefore, the effect is obtained to increasethe resolution and improve DOF without decreasing the throughput. Forexample, it is assumed that the respective processing times of T1 (waferexchange time), T2 (search alignment time), T3 (fine alignment time),and T4 (exposure time for one exposure) for an 8-inch wafer are T1: 9second, T2: 9 seconds, T3: 12 seconds, and T4: 28 seconds. When thedouble exposure is performed in accordance with the conventionaltechnique in which a series of exposure processes are performed by usingone wafer stage, there is given a throughputTHOR=3600/(T1+T2+T3+T4×2)=3600/(30+28×2)=41 [sheets/hour]. Therefore,the throughput is lowered to be up to 66% as compared with a throughput(THOR=3600/(T1+T2+T3+T4)=3600/58=62 [sheets/hour]) obtained by using aconventional apparatus in which the single exposure method is carriedout by using one wafer stage. However, when the double exposure isperformed by using the projection exposure apparatus according to thefirst embodiment of the present invention while concurrently processingT1, T2, T3, T4 in parallel to one another, there is given a throughputTHOR=3600/(28+28)=64 [sheets/hour], because it is sufficient to consideronly the exposure time. Therefore, the throughput can be improved whilemaintaining the effect to increase the resolution and improve DOF. Thenumber of points for EGA can be increased in a degree corresponding tothe long exposure time. Thus, the alignment accuracy is improved.

In the first embodiment of the present invention, explanation has beenmade for the case in which the present invention is applied to theapparatus for exposing the wafer based on the use of the double exposuremethod. However, such explanation has been made because of the followingreason. That is, as described above, when the exposure is performedtwice with the two reticles (double exposure) on the side of one of thewafer stages, during which the wafer exchange and the wafer alignmentare concurrently carried out in parallel on the side of the other waferstage which is independently movable, by using the apparatus accordingto the present invention, then the especially large effect is obtainedin that the high throughput can be obtained as compared with theconventional single exposure, and it is possible to greatly improve theresolving power. However, the range of application of the presentinvention is not limited thereto. The present invention can bepreferably applied when the exposure is performed in accordance with thesingle exposure method. For example, it is assumed that the respectiveprocessing times (T1 to T4) for an 8-inch wafer are the same as thosedescribed above. When the exposure process is performed in accordancewith the single exposure method by using the two wafer stages as in thepresent invention, if T1, T2, T3 are dealt with as one group (30 secondin total), and the concurrent process is performed for T4 (28 seconds),then there is given a throughput THOR=3600/30=120 [sheets/hour]. Thus,it is possible to obtain the high throughput which is approximately twotimes the conventional throughput (THOR=62 [sheets/hour]) in which thesingle exposure is carried out by using one wafer stage.

[Second Embodiment]

Next, the second embodiment of the present invention will be explainedwith reference to FIGS. 22 and 23. In this embodiment, constitutivecomponents which are the same as or equivalent to those referred to inthe first embodiment described above are designated by the samereference numerals, explanation of which is simplified or omitted.

As shown in FIG. 22, a projection exposure apparatus according to thesecond embodiment is characterized in that the length-measuring beamBI4Y (or BI5Y) is not deviated from the reflective surface of the stageduring the movement of the wafer stage WS1 (or WS2) from the completionposition of the alignment sequence to the start position of the exposuresequence, because the length of one side of the wafer stage WS1 (thelength of one side of WS2 is identical thereto) is longer than themutual distance BL between the length-measuring axes BI4Y and BI3Y (themutual distance between the length-measuring axes BI5Y and BI3Y isidentical thereto). Accordingly, the projection exposure apparatusaccording to the second embodiment is different from the projectionexposure apparatus according to the first embodiment described above inthat the reference mark on the fiducial mark plate can be measured afterthe reset for the interferometer as described later on. Other featuresare constructed in the same manner as the projection exposure apparatus10 according to the first embodiment described above.

FIG. 22 shows a situation in which the interferometer having thelength-measuring axis BI3Y is reset after completion of the alignmentfor the wafer W1 on the wafer stage WS1.

As also clarified from FIG. 22, the interferometers having thelength-measuring axes BI1X, BI4X for managing the position of the waferstage WS1 have their interferometer beams which are not deviated fromthe reflective surface formed on one end surface of the wafer stage WS1in the Y axis direction, after the fine alignment operation (effected byEGA described above) for the wafer W1 by the aid of the alignment system24 a. Accordingly, the main control unit 90 is operated to move thewafer stage WS1 from the alignment completion position to the positionshown in FIG. 22 at which the fiducial mark plate FM1 is located underthe projection lens PL, while monitoring measured values obtained byusing the interferometers having the length-measuring axes BI1X, BI4Y.During this process, the interferometer beam concerning thelength-measuring axis BI3Y is reflected by the reflective surface of thewafer stage WS1 immediately before positioning the fiducial mark plateFM1 just under the projection lens PL.

In this embodiment, the position of the wafer stage WS1 is controlled onthe basis of the measured values obtained by using the interferometershaving the length-measuring axes BI1X, BI4Y. Therefore, unlike the firstembodiment described above, the main control unit 90 can accuratelymanage the position of the wafer stage WS1. At this point of time (i.e.,immediately before positioning the fiducial mark plate FM1 just underthe projection lens PL), the interferometer having the length-measuringaxis BI3Y is reset. After completion of the reset, the position of thewafer stage WS1 is controlled on the basis of measured values obtainedby using the interferometers having the length-measuring axes BI1X, BI3Y(the coordinate system is changed from the first stage coordinate systemto the second stage coordinate system).

After that, the main control unit 90 is operated so that the wafer stageWS1 is positioned at the position shown in FIG. 22 to perform thedetection of the relative position between the marks MK1, MK3 on thefiducial mark plate FM1 and the projected images on the wafer surface,of the marks RMK1, RMK3 on the reticle corresponding thereto, i.e., thedetection of the relative positional relationship between the marks MK1,MK3 and the exposure position (projection center of the projectionoptical system PL) by using the exposure light beam based on the use ofthe reticle microscopes 142, 144, in the same manner as performed in thefirst embodiment described above. After that, the main control unit 90finally calculates the relative positional relationship between theexposure position and each shot in accordance with the relativepositional relationship of each shot with respect to the mark MK2 on thefiducial mark plate FM1 previously determined and the relativepositional relationship between the exposure position and the coordinateposition of the mark MK1, MK3 on the fiducial mark plate FM1. Thus, theexposure (double exposure as described above) is performed in accordancewith an obtained result (see FIG. 21).

During the exposure, the length-measuring axis BI4Y is deviated from thereflective surface depending on the exposure position, and themeasurement therewith becomes impossible. However, no inconvenienceoccurs because the length-measuring axis has been already changed forthe control of the position of the wafer stage WS1.

The operation of the exposure sequence is performed on the side of theone wafer stage WS1, during which the other wafer stage WS2 is subjectedto the positional control on the basis of the measured values obtainedby using the interferometers having the length-measuring axes BI2X,BI5Y, in which the W exchange sequence and the wafer alignment sequenceare executed. In this process, the double exposure is performed on theside of the wafer stage WS1 as described above. Therefore, the operationof the wafer exchange sequence and the wafer alignment sequenceperformed on the side of the wafer stage WS2 are completed earlier, andthen the wafer stage WS2 is in a waiting state.

At the point of time at which the exposure for all areas of the wafer W1is completed, the main control unit 90 is operated to move the waferstage WS1 to the position at which the interferometer beam concerningthe length-measuring axis BI4Y is reflected by the reflective surface ofthe wafer stage WS1 while monitoring measured values obtained by usingthe interferometers concerning the length-measuring axes BI1X, BI3Y sothat the interferometer having the length-measuring axis BI4Y is reset.After completion of the reset operation, the main control unit 90 isoperated to change the length-measuring axes for controlling the waferstage WS1 into the length-measuring axes BI1X, BI4Y again so that thewafer stage WS1 is moved to the loading position.

During the movement, the interferometer beam concerning thelength-measuring axis BI3Y is once deviated from the reflective surface,and it falls into an immeasurable state. However, no inconvenienceoccurs because the length-measuring axis has been changed to control theposition of the wafer stage

The main control unit 90 is operated to start movement of the waferstage WS2 so that the fiducial mark plate FM2 for the wafer stage WS2 ispositioned under the projection optical system PL, concurrently with themovement of the wafer stage WS1 to the loading position. During themovement, the reset of the interferometer having the length-measuringaxis BI3Y is executed in the same manner as described above. After that,the reticle microscopes 142, 144 are used to perform the detection ofthe relative positions of the marks MK1, MK3 on the fiducial mark plateFM2 and the projected images on the wafer surface, of the marks RMK1,RMK3 on the reticle corresponding thereto, i.e., the detection of therelative positional relationship between the marks MK1, MK3 and theexposure position (projection center of the projection optical systemPL), in the same manner as described above. Subsequently, the maincontrol unit 90 finally calculates the relative positional relationshipbetween the exposure position and each shot in accordance with therelative positional relationship of each shot with respect to the markMK2 on the fiducial mark plate FM2 previously determined and therelative positional relationship between the exposure position and thecoordinate position of the mark MK1, MK3 on the fiducial mark plate FM2.Thus, the exposure (double exposure as described above) is started inaccordance with an obtained result.

FIG. 23 shows a situation in which the wafer stage WS1 is moved to theloading position as described above, and the operation of the exposuresequence is performed on the side of the wafer stage WS2.

At the loading position, the mark MK2 on the fiducial mark plate FM1 islocated under the alignment system 24 a in the same manner as describedin the first embodiment. The main control unit 90 is operated to detectthe coordinate position of the mark MK2 on the first stage coordinatesystem (BI1X, BI4Y) simultaneously with completion of the wafer exchangein the same manner as described in the first embodiment. Subsequently,the EGA measurement is carried out for the mark on the wafer W1 tocalculate the coordinate position of each shot in the same coordinatesystem. That is, the relative positional relationship of each shot withrespect to the mark MK2 is calculated by subtracting the coordinateposition of the mark MK2 on the fiducial mark plate FM1 from thecoordinate position of each shot. The EGA operation is completed at thispoint of time, and the system waits for completion of the exposure forthe wafer W2 on the wafer stage WS2 to make a change again to the stateshown in FIG. 22.

According to the projection exposure apparatus concerning the secondembodiment of the present invention explained above, it is possible toobtain effects equivalent to those obtained in the first embodimentdescribed above. Besides, the reflection is allowed to occursimultaneously on the reflective surface of the wafer stage for thelength-measuring axes used before and after the change respectivelyduring the movement of the stage when the change is made to theoperation of the exposure sequence after completion of the operation ofthe alignment sequence. Further, the reflection is allowed to occursimultaneously on the reflective surface of the wafer stage for thelength-measuring axes used before and after the change respectivelyduring the movement of the stage when the change is made to theoperation of the wafer exchange/alignment sequence after completion ofthe operation of the exposure sequence. Accordingly, it is possible thatthe mark on the fiducial mark plate is measured after the reset of thelength-measuring interferometer by using the exposure light beamalignment sensor (reticle alignment microscope 142, 144) by the aid ofthe projection optical system PL, the reset for the length-measuringinterferometer is executed prior to the wafer exchange, and the mark onthe fiducial mark plate is measured after completion of the waferexchange by using the off-axis alignment sensor (alignment system 24 a,24 b). Therefore, the interferometer to be used for the stage controlcan be changed to the interferometer having the length-measuring axis tobe used for the operation after the change, during the change from thealignment operation based on the use of each alignment system to theexposure operation based on the use of the projection optical system PL,and during the change from the exposure operation based on the use ofthe projection optical system PL to the wafer exchange operation.Accordingly, it is possible to further improve the throughput, ascompared with the case of the first embodiment in which thelength-measuring axis is changed simultaneously with the measurement ofthe mark on the fiducial mark plate.

In the first and second embodiments described above, explanation hasbeen made for the case in which the present invention is applied to theapparatus for exposing the wafer based on the use of the double exposuremethod. However, such explanation has been made because of the followingreason. That is, as described above, when the exposure is performedtwice with the two reticles (double exposure) on the side of one of thewafer stages, during which the wafer exchange and the wafer alignmentare concurrently carried out in parallel on the side of the other waferstage which is independently movable, by using the apparatus accordingto the present invention, then the especially large effect is obtainedin that the high throughput can be obtained as compared with theconventional single exposure, and it is possible to greatly improve theresolving power. However, the range of application of the presentinvention is not limited thereto. The present invention can bepreferably applied when the exposure is performed in accordance with thesingle exposure method. For example, it is assumed that the respectiveprocessing times (T1 to T4) for an 8-inch wafer are the same as thosedescribed above. When the exposure process is performed in accordancewith the single exposure method by using the two wafer stages as in thepresent invention, if T1, T2, T3 are dealt with as one group (30 secondin total), and the concurrent process is performed for T4 (28 seconds),then there is given a throughput THOR=3600/30=120 [sheets/hour]. Thus,it is possible to obtain the high throughput which is approximately twotimes the throughput (THOR=62 [sheets/hour]) of the conventionalapparatus in which the single exposure is carried out by using one waferstage.

In the embodiment described above, explanation has been made for thecase in which the scanning exposure is performed in accordance with thestep-and-scan system. However, the present invention is not limitedthereto. It is a matter of course that the present invention can beequivalently applied to a case in which the stationary exposure isperformed in accordance with the step-and-repeat system, as well asthose based on the use of the EB exposure apparatus and the X-rayexposure apparatus, and a process of the stitching exposure in which achip is combined with another chip.

[Third embodiment]

In the first embodiment of the present invention, the differentoperations are concurrently processed in parallel to one another byusing the two wafer stages WS1, WS2. Therefore, there is a possibilitythat the operation performed on the one stage gives influence(disturbance) to the operation of the other stage. For this reason, asdescribed above, it is necessary to adjust the timing for the operationsperformed on the two stages WS1, WS2.

In this embodiment, explanation will be made for the timing adjustmentfor the operations performed on the two stages WS1, WS2, with referenceto FIGS. 11, 12 and 24.

As explained in the first embodiment, FIG. 11 shows an example of thetiming of the exposure sequence for successively exposing the respectiveshot areas on the wafer W1 held on the stage WS1. FIG. 12 shows thetiming of the alignment sequence for the wafer W2 held on the stage WS2,which is processed concurrently in parallel thereto.

As described above, the operations performed on the two stages WS1, WS2include the disturbance factor operation in which the operationperformed on one of the stages affects the operation performed on theother stage, and the non-disturbance factor operation in which theoperation performed on one of the stages does no affect the operationperformed on the other stage in a reverse manner. Accordingly, in theembodiment of the present invention, the operations to be concurrentlyprocessed are divided into disturbance factor operations andnon-disturbance factor operations to achieve the timing adjustment sothat a disturbance factor operation is successfully performedsimultaneously with another disturbance factor operations, and anon-disturbance factor operations is successfully performedsimultaneously with another non-disturbance factor operation.

Upon the start of the timing adjustment for the operations as shown inFIG. 24, at first, the main control unit 90 is operated so that theexposure start position of the wafer W1 held on the stage WS1 isadjusted to be at the exposure position of the projection optical systemPL for performing the exposure operation, and the detection startposition for the mark on the wafer W2 held on the stage WS2 is adjustedto be at the detection position of the alignment system 24 b forperforming the alignment operation. In this state, the main control unit90 waits for the input of a start command for the operation to beexecuted on the stage.

When the operation start command is inputted, the main control unit 90judges in a step S2 whether or not the exposure operation performed onthe wafer W2 is an operation not to behave as a disturbance factor(non-disturbance factor operation). The scanning exposure operationperformed on the wafer W1 is a non-disturbance factor operation whichdoes not affect the other stage, because the wafer W1 and the reticle Rare subjected to synchronized scanning at a constant velocity. However,during the stepping operation corresponding to the movement between shotareas and across acceleration and deceleration areas existing before andafter the constant velocity scanning, the scanning exposure operationbehaves as a disturbance factor operation, because the stage WS1 isdriven in an accelerating or decelerating manner. When the alignmentoperation is performed on the wafer W2, the operation behaves as anon-disturbance factor operation which does not affect the other stage,because the mark measurement is performed in a stationary state in whichthe mark is adjusted to the alignment system. However, the steppingoperation corresponding to the movement between the marks to be measuredbehaves as a disturbance factor operation, because the stage WS2 isdriven in an accelerating or decelerating manner.

Accordingly, in the step S2, when the operation performed on the waferW1 is a non-disturbance factor operation such as the operation duringthe scanning exposure, it is necessary to exclude the disturbance factoroperation from the operation concurrently processed on the wafer W2,because the exposure accuracy is lowered if the disturbance factoroperation such as an stepping operation is performed on the other stageWS2. Therefore, if the judgment in the step S2 is affirmed, the maincontrol unit 90 judges whether or not the operation to be performed nexton the wafer W2 is a non-disturbance factor operation which issimultaneously executable (step S4). The non-disturbance factoroperation, which is simultaneously executable on the wafer W2, includes,for example, a mark-detecting operation performed in a stationary state.In this embodiment, the non-disturbance factor operation as describedabove is executed simultaneously with another non-disturbance factoroperation (step S6).

In the step S4, if the operation timing is deviated, or if there is nomark to be detected, then the routine proceeds to a step S8 to executethe scanning exposure operation on the wafer W1, and the processingoperation on the wafer W2 is allowed to wait, because there is nonon-disturbance factor operation which is simultaneously executable. Themain control unit 90 judges in a step S10 whether or not thenon-disturbance factor operations on the wafers W1, W2 are completed. Ifthe operations are not completed, the routine returns to the step S6 torepeatedly perform the operation as described above. If the operationsare completed, the presence or absence of the next processing operationis judged in the next step S12. If the next processing operation ispresent in the step S12, the routine returns to the step S2 to repeatthe operation as described above. If the next processing operation isabsent, the routine ends.

In the step S2, when the stage WS1 is subjected to stepping movement tomake movement between shot areas on the wafer W1, then the main controlunit 90 judges such movement to be a disturbance factor operation, andthe routine proceeds to a step S14. The main control unit 90 judgeswhether or not an operation to be performed next on the wafer W2 is asimultaneously executable disturbance factor operation (step S14). Thedisturbance factor operation, which is simultaneously executable on thewafer W2, includes, for example, stepping movement between measurementmarks. Therefore, the disturbance factor operation as described above isexecuted in a step S16 simultaneously with another disturbance factoroperation.

In the step S14, if the operation timing is deviated, or if there is nostepping movement between measurement marks, then there is nosimultaneously executable disturbance factor operation. Therefore, theroutine proceeds to a step S18 to execute the stepping operation on thewafer W1, and the processing operation on the wafer W2 is allowed towait. The main control unit 90 judges whether or not the disturbancefactor operations on the wafers W1, W2 are completed in a step S20. Ifthe operations are not completed, the routine returns to the step S16 torepeatedly perform the operation as described above. If the operationsare completed, the routine proceeds to the step S12 to judge thepresence or absence of any operation to be processed next. In the stepS12, if there is any operation to be processed next, the routine returnsto the step S2 again to repeat the operation as described above. Ifthere is no operation to be processed next, the routine ends.

Next, explanation will be made for an example of adjustment for theoperation timing on the two wafers W1, W2 with reference to FIGS. 11 and12. At first, on the wafer W1 shown in FIG. 11, the scanning exposureoperation (non-disturbance factor operation) indicated by the operationnumbers of “1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23” is successivelyperformed along arrows depicted by chain lines. It is understood that onthe wafer W2 shown in FIG. 12, the mark-measuring operation(non-disturbance factor operation) is performed in a stationary state atpositions of respective alignment marks indicated by the operationnumbers of “1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, . . . ” insynchronization with the scanning exposure operation. On the other hand,no disturbance arises in the alignment sequence because the constantvelocity movement is performed during the scanning exposure, and henceit is possible to perform highly accurate measurement.

In the alignment sequence (EGA) shown in FIG. 12, the alignment marksare measured at two points for each of the shot areas. Some of thealignment marks shown in FIG. 12 do not have operation numbers, becauseof the following reason. That is, for example, when an upper mark(before the operation number 4 in FIG. 12) of the next alignment shot isdisposed in the vicinity of a lower mark (having the operation number 3in FIG. 12) of the first alignment shot, then the upper mark is measuredsimultaneously with the lower mark, or the upper mark is measured afterthe wafer stage WS2 is moved by a minute distance at an acceleration ofa degree at which the synchronization accuracy is not affected therebywith respect to the other wafer stage WS1. Therefore, these marks areindicated by the identical operation number (3 in this case). It isassumed that the measurement is performed in the same manner asdescribed above for the alignment marks of the operation numbers otherthan the above.

On the wafer W1 shown in FIG. 11, the stepping movement (disturbancefactor operation) between shot areas to be subjected to the scanningexposure is performed at the timing indicated by the operation numbersof “2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22”. On the wafer W2 shown inFIG. 12, the stepping movement (disturbance factor operation) betweenmeasurement marks is performed at the timing indicated by the operationnumbers of “2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, . . . ” insynchronization with the stepping movement of the wafer W1.

As shown in FIG. 7, when the wafer exchange operation is performed forthe wafer W1, and the scanning exposure is performed for the wafer W2,then the disturbance factor arises, for example, in the vibrationgenerated when the wafer W1 is delivered from the first load arm 188 tothe center-up 180. However, in this case, it is assumed that the maincontrol unit 90 performs the timing adjustment so that the wafer W2 isallowed to wait before and after the scanning exposure. Further, adisturbance factor arises concerning the wafer W2 in the process ofacceleration or deceleration before or after the arrival at a constantvelocity for the synchronized scanning for the wafer and the reticle.Therefore, the timing adjustment may be performed so that the wafer W1is delivered in synchronization with this process.

As described above, the main control unit 90 is operated to adjust theoperation timing so that the operations which behave as disturbancefactors are performed in synchronization with each other as far aspossible, or the operations which behave as non-disturbance factors areperformed in synchronization with each other as far as possible, of theoperations to be concurrently processed on the wafers W1, W2 held on thetwo stages respectively. Thus, it is possible to avoid the mutualinfluence which would be otherwise exerted by the disturbance, even whenthe respective operations are concurrently processed in parallel to oneanother on the two stages. All of the timing adjustment described aboveis performed by using the main control unit 90.

Next, explanation will be made for the interference condition todetermine whether or not the two wafer stages WS1, WS2 make contact witheach other, with reference to FIGS. 25A and 25B. FIG. 25A shows a statein which the wafer stage WS2 is located under the projection opticalsystem PL, and the reference mark on the fiducial mark plate FM2 on thewafer stage WS2 is observed by using the TTR alignment system describedabove. It is assumed that the coordinate position (x, y) of the waferstage WS2 at this time is (0, 0). Assuming that the X coordinate at theleft end of the wafer stage WS2 is (−Wa) with respect to the referencemark on the fiducial mark plate FM2, the coordinate position at the leftend of the wafer stage WS2 is (−Wa, y).

The coordinate position concerning the wafer stage WS1 is assumed asfollows in the same manner as described above. That is, the coordinateposition, which is obtained when the reference mark is measured bymoving the fiducial mark plate FM1 on the wafer stage WS1 up to theposition under the projection optical system PL, is (0, 0). The amountof movement from this position to the position of the wafer stage WS1shown in FIG. 25A is (−Xb). The X coordinate at the right end of thewafer stage WS1 with respect to the reference mark on the fiducial markplate FM1 is (Wb). On this assumption, the coordinate position at theright end of the wafer stage WS1 is (−Xb+Wb, y).

The condition, under which the both wafer stages WS1, WS2 make nointerference with each other, lies in a state in which the left end ofthe wafer stage WS2 makes no contact with the right end of the waferstage WS1. Therefore, this condition may be represented by a conditionalexpression of 0<−Wa−(−Xb+Wb).

On the contrary, FIG. 25B assumes a state in which the wafer stage WS1is moved in the direction of (−Xa) by a predetermined distance from thestate shown in FIG. 25A, and the two wafer stages WS1, WS2 areoverlapped with each other (actually, the two wafer stages are notoverlapped with each other, however, when the respective wafer stagesare independently controlled, there is a possibility that target valuesfor the respective stages may be set as shown in FIG. 25B). Thecoordinate position at the left end of the wafer stage WS2 is (−Xa−Wa,y). The condition, under which the both wafer stages WS1, WS2 causeinterference with each other, lies in a state in which the left end ofthe wafer stage WS2 is contacted or overlapped with the right end of thewafer stage WS1. Therefore, this condition may be represented by aconditional expression depicted by 0>−Xa−Wa−(−Xb+Wb).

The conditional expression may be represented by the following generalexpression by using a certain reference point based on the use of thesame coordinate:

Wa+Wb<Xb−Xa  conditional expression 1

If the conditional expression 1 is satisfied, the two wafer stages canbe freely moved without any interference with each other.

On the other hand, if the following conditional expression 2 issatisfied, the two wafer stages make contact with each other to causeinterference.

Wa+Wb≧Xb−Xa  conditional expression 2

Therefore, the main control unit 90 controls the movement of therespective wafer stages WS1, WS2 to satisfy the conditional expression 1as far as possible, while if a situation in which the conditionalexpression 2 is satisfied is postulated, it is necessary to make controlin order to allow any one of the stages to wait so that the occurrenceof mutual interference between the stages is avoided. The conditionalexpressions 1 and 2 have been explained as two separate individuals forthe purpose of more comprehensive explanation. However, the twoconditional expressions are substantially one conditional expression,because there is a relationship in which one of the conditionalexpressions is in contradiction to the other.

Explanation will be made with reference to a flow chart shown in FIG. 26for a sequence to perform control of the movement without causing anyinterference between the both wafer stages by using the main controlunit 90 on the basis of the conditional expression described above. Atfirst, upon the start of the control operation, the main control unit 90measures the coordinate positions of the two wafer stages WS1, WS2 byusing values obtained by the interferometers based on the use of theorigin (0, 0) of the same reference position (position of the opticalaxis of the projection optical system PL in this case). The conditionalexpression 1, which is previously stored in the memory 91, issubstituted with necessary parameters (Wa and Wb in this case).

When the stage movement control is started, the main control unit 90grasps the present positions of the two wafer stages WS1, WS2 on thebasis of values obtained by using the length-measuring axes (forexample, BI1X, BI2X) of the interferometers. The main control unit 90 isable to calculate and postulate the coordinate positions of the stagesWS1, WS2 in future, on the basis of driving target values inputted intothe stage control unit 38. The main control unit 90 determines, fromthese coordinate positions, the movement direction and the movementdistance (Xb and Xa in this embodiment) of the two stages WS1, WS2 withrespect to the reference position to substitute the conditionalexpression 1 therewith. Thus, it is possible to judge whether or not theconditional expression 1 (Wa+Wb<Xb−Xa) is satisfied (step S30).

If the conditional expression 1 is satisfied, no mutual interferenceoccurs between the two wafer stages WS1, WS2. Accordingly, the bothstages WS1, WS2 can be independently moved and controlled (step S32).

If the conditional expression 1 is not satisfied in the step S30, theinterference occurs between the wafer stages WS1 and WS2. Therefore, themain control unit 90 compares the time until completion of the operationperformed on the stage WS1 with that on the stage WS2 (step S34). If theoperation on the stage WS1 is completed earlier, then the main controlunit 90 allows the stage WS1 to wait, and the wafer stage WS2 ispreferentially moved and controlled (step S36). During the control ofthe movement of the wafer stage WS2, the main control unit 90 alwaysjudges whether or not a situation is given, in which the conditionalexpression 1 is satisfied (step S38). During the period in which theconditional expression 1 is not satisfied, the routine returns to thestep S36 to preferentially move and control the wafer stage WS2. If theconditional expression 1 is satisfied in the step S38, the main controlunit 90 is operated so that the waiting state of the wafer stage WS1 iscanceled (step S40) to independently move and control the wafer stagesWS1, WS2 respectively (step S32).

In the step S34, if the operation of the stage WS2 is completed earlier,then the main control unit 90 allows the stage WS2 to wait, and thewafer stage WS1 is preferentially moved and controlled (step S42).During the control of the movement of the wafer stage WS1, the maincontrol unit 90 always judges whether or not a situation is given, inwhich the conditional expression 1 is satisfied (step S44). During theperiod in which the conditional expression 1 is not satisfied, theroutine returns to the step S42 to preferentially move and control thewafer stage WS1. If a state is given, in which the conditionalexpression 1 is satisfied in the step S44, the waiting state of thewafer stage WS2 is canceled by the main control unit 90 (step S40) toindependently move and control the wafer stages WS1, WS2 respectively(step S32).

If the stage movement control is continuously performed by using themain control unit 90, the routine returns from the step S46 to the stepS30 to repeatedly perform the movement control as described above. Ifthe stage movement control is not performed, the control operation isended.

As described above, the main control unit 90 controls the movement ofthe two stages WS1, WS2 by the aid of the conditional expression and thestage control unit 38. Thus, it is possible to prevent the both stagesfrom mutual interference.

When the double exposure method described above is carried out, theoperation completion time on the stage for performing the exposureoperation is later than that on the stage for performing the alignmentoperation, because the exposure operation is repeated twice. For thisreason, when the mutual interference occurs between the stages, then thestage for the alignment, on which the operation is completed earlier, isallowed to wait, and the stage for the exposure is preferentially moved.

However, on the stage for the alignment, it is allowable to concurrentlyperform not only the fine alignment operation as described above butalso the wafer exchange operation, the search alignment operation, andoperations other than the above in parallel to one another. Therefore,it is desirable that the operation time on the stage for the alignmentis shortened as short as possible.

Accordingly, as shown in FIG. 27B, the most efficient stepping order (E1to E12) is set for the wafer W2 for performing the exposure operation,because the exposure operation constitutes the rate-limiting conditionfor the throughput. On the contrary, as shown in FIG. 27A, several shotsof the exposure shots are selected as sample shots on the wafer W1 forperforming the alignment operation based on EGA. In this embodiment, itis assumed, for example, that four shots indicated by symbol “A” areselected. The stepping order on the alignment side (W1) is determined tomake movement corresponding to the stepping order in the exposureoperation for the wafer W2, as on the wafer W1 disposed on the alignmentside as shown in FIG. 28A. As for the wafer W2 shown in FIG. 28B,operations during the exposure, for which the influence of disturbanceshould be suppressed, are designated by numerical numbers (1 to 12) ,while stepping operations which are not affected by disturbance areindicated by arrows (→).

As shown in FIG. 28A, when the fine alignment operation based on EGA isperformed on the wafer W1, the movement order is determined so that thealignment operation is performed for the shot areas corresponding tothose on the wafer W2 to perform the scanning exposure as shown in FIG.17B for the operation numbers 1 to 5. Accordingly, when the movementorder of the alignment shots is made to be the same as that for theexposure shots, the two stages are moved in parallel to one anotherwhile maintaining a constant spacing distance therebetween. Therefore,it is possible to control the movement without satisfying theinterference condition.

In the case of the wafer W1 shown in FIG. 28A, the alignment order isdetermined as follows. That is, when the operation number is moved from5 to 6 in a stepping manner, the operation skips to the shot area A3located thereover by one row, and when the operation number becomes 7,the operation skips to the shot area A4. This is because of thefollowing reason. That is, when the shot area, which is indicated by theoperation number 6 or 7 on the wafer W2 shown in FIG. 28B to besubjected to the scanning exposure, is disposed under the projectionoptical system PL, the wafer stage WS2 is at a position spaced apartfrom the wafer stage WS1 (the wafer W2 is disposed at the most rightwardposition concerning the position of the operation number 6 or 7, becausethe alignment system is fixedly secured, and the wafer is moved).Accordingly, it is possible to relatively freely move the wafer stageWS1 for performing the alignment operation. As described above, the finealignment time can be further shortened by moving the wafer W1 as shownin FIG. 28A to perform the alignment operation.

Alternatively, when an alignment mark at one point is detected for everyone shot area to use all shot areas as sample shots, unlike the sampleshots used in the alignment sequence described above, it is possible toavoid deterioration of throughput. In this procedure, the alignmentmarks in the shot areas corresponding to the exposure order on the waferW2 are successively measured. The occurrence of interference between thestages disappears as described above. Further, when such EGA isperformed, it is possible to expect further improvement in alignmentaccuracy owing to the averaging effect.

As explained above, according to the projection exposure apparatus 10concerning the embodiment of the present invention, the operations ofthe both stages are controlled so that the operations which behave asdisturbance factors are performed in synchronization with each other, orthe operations which do not behave as disturbance factors are performedin synchronization with each other, of the operations to be performed onthe two wafer stages which independently hold the two wafersrespectively. Accordingly, the alignment operation can be processedconcurrently with the exposure operation without decreasing thesynchronization accuracy when the scanning exposure is performed andwithout decreasing the mark measurement accuracy when the alignment isperformed. Thus, it is possible to improve the throughput.

According to the embodiment described above, when the two wafer stagesare independently moved and controlled in the XY two-dimensionaldirection, then the condition of interference between the two waferstages (interference condition) is previously stored, and the movementis controlled so that the interference condition is not satisfied as faras possible. Accordingly, the movement ranges of the both stages can beoverlapped with each other. Therefore, it is possible to decrease thefoot print.

According to the embodiment described above, when the two wafer stagesare independently moved in the XY direction, if the interferencecondition is satisfied in each of the stages, then the stage on whichthe operation is completed earlier is allowed to wait until theoperation is changed, and the other stage is preferentially subjected tothe movement control. Accordingly, it is possible to avoid theinterference between the stages without deteriorating the throughput.

According to the embodiment described above, when arbitrary shots areselected as alignment shots from a plurality of shot areas on the waferto be used in the alignment sequence for performing the markmeasurement, the order of measurement of the alignment shots isdetermined so that the interference is avoided between the both stagesas less as possible. Accordingly, it is possible to appropriatelysuppress the case of the interference condition between the stages andthe case in which one of the stages is allowed to wait as describedabove.

In the embodiment described above, the order of alignment shots and theorder of exposure shots are determined so that the two wafer stages aremoved in the same direction, if possible. Accordingly, the range ofmovement of the two wafer stages can be decreased as small as possible,and it is possible to miniaturize the apparatus. However, when theprojection optical system and the alignment system can be installedwhile they are spaced apart from each other by a certain distance, thenthe two wafer stages, which are movable on the base pedestal, may bemoved in mutually opposite directions in a left-right symmetric manner.Accordingly, the loads act on the vibration-preventive mechanism forsupporting the base pedestal so that the loads are offset with eachother. Therefore, the output of the vibration-preventive mechanism canbe suppressed to be small, the inclination of the stage and theoccurrence of vibration are decreased, and the vibration convergencetime can be shortened. Thus, it is possible to further improve theoperation accuracy and the throughput.

In the embodiment described above, explanation has been made for thecase in which the alignment operation and the wafer exchange operationare processed concurrently with the exposure operation. Of course, thepresent invention is not limited thereto. The operation, which may beperformed concurrently with the exposure operation, includes, forexample, base line check (BCHK). A sequence such as those forcalibration which is performed every time when the wafer exchange isperformed may be processed concurrently with the exposure operation inthe same manner as described above.

[Fourth Embodiment]

Next, the fourth embodiment of the present invention will be explainedwith reference to FIGS. 29 to 43. In the fourth embodiment of thepresent invention, the pre-measurement AF/AL is performed by using onewafer stage WS, while the focus/leveling control is performed on thebasis of obtained results of the measurement so that the exposureprocess is executed.

FIG. 29 shows a schematic arrangement of a projection exposure apparatus214 according to the fourth embodiment. The projection exposureapparatus 214 is a scanning exposure type projection exposure apparatusbased on the step-and-scan system in the same manner as described in thefirst embodiment. Basic constitutive components of the projectionexposure apparatus 214 are the same as those of the projection exposureapparatus 10 according to the first embodiment shown in FIG. 1. The sameparts or components are designated by the same reference numerals,explanation for the construction of which will be omitted. Theprojection exposure apparatus 214 is different from the projectionexposure apparatus 10 of the first embodiment in the following points.That is, the wafer stage WS is constructed as one individual, and theAF/AL systems for measuring the surface position on the wafer W forpre-measurement control are provided on one side and the other side ofthe exposure area IF in the scanning direction. Further, the projectionexposure apparatus 214 comprises an irradiating optical system 151 and alight-collecting optical system 161 based on the oblique incidencesystem constructed so that a plurality of detecting points are arrangedover a range wider than the width of the exposure area IF in thenon-scanning direction. Moreover, the wafer stage WS according to thefourth embodiment of the present invention is provided with a Z-levelingstage LS as a substrate-driving system for making fine driving andoblique driving in the Z axis direction while holding the wafer W.

As viewed in FIG. 30 illustrating, in a perspective view, thearrangement of the AF detecting points for the pre-measurement controlwith respect to the exposure area IF, a detecting area AFE (see FIG.35), which is constructed by the detecting points AF1 to AF9 in thenon-scanning direction (±X direction), is provided in the scanningdirection (+Y direction) for the exposure area IF. The detecting areaAFE is arranged over a range larger than the width of the exposure areaIF in the non-scanning direction. Further, a detecting area ABE (seeFIG. 35), which is constructed by the detecting points AB1 to AB9 in thenon-scanning direction (±X direction), is provided in the scanningdirection (−Y direction) for the exposure area IF. The detecting area.ABE is arranged over a range larger than the width of the exposure areaIF in the non-scanning direction. The detecting points AF1 to AF9 andthe detecting points AB1 to AB9 are arranged on the front sides in thescanning directions (+Y direction, −Y direction) for scanning theexposure area IF respectively. The relative position, which indicatesthe degree of discrepancy of the surface of the wafer W at each of thedetecting points with respect to a predetermined reference plane, isdetected prior to the exposure for the shot area.

FIG. 31 shows a side view of FIG. 30 as viewed in the scanningdirection, FIG. 32 shows a plan view of FIG. 31, and FIG. 33 shows aside view of FIG. 32 as viewed in the non-scanning direction.

As shown in FIGS. 32 and 33, the light beams, which are radiated fromthe irradiating optical systems 151 a, 151 b of the oblique incidencetype AF/AL system, form the detecting points AB1 to AB9 and thedetecting points AF1 to AF9 extending over the surface of the wafer W inthe non-scanning direction. The light beams reflected by the surface ofthe wafer W are received by the light-collecting optical systems 161 a,161 b of the oblique incidence type AF/AL system. This arrangement isprovided because of the following reason. That is, in general, it isimpossible to perform measurement for the inside of the exposure area IFby using the oblique incidence AF system, because the working distancebetween the wafer W and the lower surface of the projection lens isnarrowed in accordance with the increase in N.A. (numerical aperture) ofthe projection lens of the projection optical system PL. However, in thepresent invention, even in such a case, it is intended to execute thecomplete pre-measurement.

As shown in FIGS. 31 and 33, the fourth embodiment of the presentinvention is constructed as follows. That is, the shape of theprojection optical system PL in the vicinity of its lower end is aninverted truncated cone. A plurality of irradiating light beams comingfrom the irradiating optical systems 151 a, 151 b are radiated onto therespective positions of the detecting points on the wafer W. Thereflected light beams coming from the surface of the wafer W passthrough the both sides of the projection optical system PL, and they arereceived by the light-collecting optical systems 161 a, 161 b. Thearrangement as described above is provided in order that the AF lightbeams are not intercepted in the vicinity of the lower end of theprojection optical system PL. A parallel flat plate 216 having arectangular configuration is disposed at the lowermost plane of theprojection optical system PL in conformity with the scanning directionin order to harmonize the extending portion of N.A. with the directionof 45° of the projection optical system PL, and in order to correct theaberration of the projection lens which constructs the projectionoptical system PL. The AF detecting points, which extendone-dimensionally in the non-scanning direction, are arranged at twoplaces as those for +Y scanning and −Y scanning, in front of and at theback of the parallel flat plate 216 in the scanning direction. Forexample, when this system is compared with a two-dimensional detectiontype AF mechanism as described in Japanese Laid-open Patent PublicationNo. 6-283403 corresponding to U.S. Pat. No. 5,448,332, then the AFmeasurement cannot be performed at the exposure position, while it ispossible to form a long spot group extending in the non-scanningdirection, and the detecting points are arranged one-dimensionally.Accordingly, this system is advantageous in that the offset error, whichis caused by intra-plane curvature of the respective AF spots in the Zdirection, can be easily corrected. Further, for example, when a methodfor forming the interference fringe in the non-scanning direction bymeans of two-directional incidence is adopted, the present invention iseasily and advantageously applied, because the present invention residesin the pre-measurement control method for the one-dimensional processfor detecting the AF/AL position by means of one-dimensional imageprocessing in accordance with the distance error and the positionalvariation of the interference fringe. Moreover, the light beams aredivided into those for the two places of the detection areas AFE, ABE.Accordingly, when a cover which does not intercept the respective lightbeams is provided so that the AF/AL accuracy, which varies depending onthe temperature change, is improved by allowing a temperature-controlledgas to flow through the inside of the cover, then an effect is obtainedin that the detection error is further reduced.

Next, explanation will be made for the pre-measurement control based onthe use of the projection exposure apparatus 214 according to the fourthembodiment of the present invention, in which the shot array is largerthan the outer circumference of the wafer W. For example, FIG. 42 showsComparative Example concerning pre-measurement control, in which theshot array is larger than the outer circumference of the wafer W. InFIG. 42, AF detecting points AF1 to AF5, which are arranged in thenon-scanning direction, are disposed on the front side in the scanningdirection with respect to the exposure area IF subjected to scanningexposure (in the direction indicated upwardly by an arrow in the planeof the paper; actually, the exposure area IF and the AF detecting pointsAF1 to AF5 are fixed, and the wafer W is scanned with respect thereto,however, for convenience, the illustration is given such that theexposure area IF and the AF detecting points shown in the drawing arescanned with respect to the wafer surface). A detecting area AFB, whichis constructed by the AF detecting points AF1 to AF5, is provided toperform AF measurement for executing complete pre-measurement control.The width of the detecting area AFB is approximately the same as thewidth of the exposure area IF in the non-scanning direction. When thepre-measurement control is made by using the projection exposureapparatus constructed as shown in FIG. 42 (Comparative Example), AFoutput values ranging from AF1 to AF5 are obtained in accordance withthe movement of the stage as shown in FIG. 43. In FIG. 43, thehorizontal axis indicates the movement time [t] of the stage, and thevertical axis indicates the relative position [μm] in the Z directionwith respect to the surface position of the wafer. As shown in thediagram in FIG. 43, the detecting points AF5 to AF3, which overlap thesurface of the wafer W, gradually represent the surface position of thewafer in accordance with the movement of the detecting points in thescanning direction. However, the detecting points AF2 and AF1 do notpass over the wafer surface until the end. Therefore, no normal outputvalue is obtained for the detecting points AF2 and AF1. As describedabove, when it is intended to carry out the pre-measurement control forall shot areas based on the five-point measurement as illustrated inComparative Example shown in FIGS. 42 and 43, then an error occurs forthe shot area in the vicinity of the outer circumference of the wafer,and it is impossible to perform the AF/AL control in some cases. Inorder to avoid this inconvenience, it is necessary to make change intoan AF/AL control sequence for incomplete shot areas so that thepre-measurement control is carried out while performing scanning fromthe inside to the outside of the wafer W, or the exposure process iscarried out by using measurement data on the surface position of thewafer concerning the adjacent shot.

On the contrary, as shown in FIG. 30, in the fourth embodiment of thepresent invention, the width of the AF detecting points in thenon-scanning direction is widened as compared with the exposure area IF,and thus the surface position of the wafer of the adjacent shot area canbe measured. Accordingly, the pre-measurement control, which scarcelysuffers from error, is performed by utilizing the result of themeasurement.

FIG. 34 shows a plan view of the wafer W, which explains thepre-measurement control method based on the use of the AF/AL systemaccording to the fourth embodiment. FIG. 34 shows grouping forrespective shot areas, designated when the pre-measurement control iscarried out in an order in which the wafer W can be exposed mostquickly. FIG. 35 shows a positional relationship between the exposurearea IF and the AF detecting points during the focus measurement. Inthis embodiment, it is previously determined that what AF detectingpoints (AF1 to AF9, AB1 to AB9) are used for each of the shot areas toperform the AF measurement, by making grouping such as “A, B, C, D, E,F, AF, AB”, so as to previously determine the positions of the detectingpoints used for respective groups, as shown in a table in FIG. 36. Inthe table shown in FIG. 36, the position of the AF detecting point (AF1to AF9, AB1 to AB9) to be used is indicated in the lateral direction,and the name of the group obtained by grouping the respective shot areasis indicated in the vertical direction. The control is made by the maincontrol unit 90 so that the pre-measurement control is performed byusing the AF detecting points (sensors) affixed with circle symbols atthe crossing positions thereof.

For example, FIG. 37 shows the positional relationship at the point oftime to start the pre-measurement control for the wafer surface and theAF detecting points used when the shot area 212 of the group A isexposed (for example, when the shot area located at the upper-left endin FIG. 34 is exposed). In this case, the control is made by the maincontrol unit 90 so as to use the AF detecting points AF7, AF8, AF9 whichare located at positions separated from the exposure area IF by adistance L in the scanning direction. In this procedure, at the point oftime to start the pre-measurement control shown in FIG. 37, all of thethree AF detecting points (AF7, AF8, AF9) designated by the main controlunit 90 are located on the wafer surface. Therefore, the pre-measurementcontrol is performed on the basis of measured values measured at thethree AF detecting points AF7, AF8, AF9 until completion of the exposurefor the shot area 212 indicated by broken lines.

The process shown in FIGS. 36 and 37 resides in the “AF detecting pointfixation method” in which the AF detecting points to be used arepreviously fixed corresponding to the shot area. In the example shown inFIG. 37, only the detecting point AF7 is actually measured in the shotarea 212. The AF/AL control based on the pre-measurement can beperformed by using measured values for the detecting points AF8, AF9disposed on the adjacent shot area.

When no incomplete AF detecting point is included in the shot areaduring the pre-measurement control, namely when the group AF or thegroup AB shown in FIG. 34 is processed, the measurement is performed byusing only the detecting points AF3 to AF7 and AB3 to AB7 located in theshot area designated in the table in FIG. 36. The detecting points AF1,AF2, AF8, AF9 located outside the shot area are not used.

In the case of the group E shown in FIG. 34, the measurement isperformed by using the detecting points AF1 to AF5 as designated in thetable in FIG. 36. In the case of the group E, the detecting points AF6,AF7 can be measured on the way of the process of the pre-measurementcontrol as shown in FIG. 34. Accordingly, the accuracy is increased whenmeasured values for the detecting points AF6, AF7 are used. However, anadvantage is obtained in that the control process effected by the maincontrol unit 90 can be simplified in a degree corresponding to thenonnecessity to change the AF detecting point used in one time ofexposure operation during setting for the shot array. Therefore, if thecontrol process has a certain margin, it is preferable that the measuredvalues for the detecting points AF6, AF7 are used to perform more highlyaccurate focus/leveling control.

Next, explanation will be made for pre-measurement control methods otherthan the above. FIG. 38 lies in the “AF detecting point movement type”in which the focus measurement for the wafer surface is performed for apredetermined shot area by moving the AF detecting points in conformitywith successive movement in the scanning direction of the sensorscapable of performing AF measurement on the surface of the wafer Wwithout changing the number of AF detecting points to be used. Inprinciple, this method is the most excellent measuring method having thehighest accuracy, of AF measurement methods based on the pre-measurementcontrol. When the “AF detecting point movement type” is carried out, themain control unit 90 makes control so that the AF detecting points arechanged on the basis of positional information on the outercircumference of the wafer, positional information on the AF detectingpoints, and positional information on the shot area as the exposureobjective, in order to recognize what AF detecting point overlaps theeffective area located inside the prohibition zone defined at thecircumferential edge portion of the wafer W, while moving the wafer Winthe scanning direction. For example, in the case of the procedure shownin FIG. 38, the measurement is firstly performed by using threedetecting points AF7, AF8, AF9. Secondly, detecting points AF6, AF7, AF8are used. Thirdly, detecting points AF5, AF6, AF7 are used. Finally,detecting points AF4, AF5, AF6 are used. In such a way, the sensors arechanged so as to select the three detecting points, if possible, withinthe shot area 212 within the effective area on the wafer surface.Accordingly, even when the outer circumferential portion of the wafer W,at which the shot area is provided, is subjected to scanning exposurefrom the outside to the inside by moving the exposure area IF (actually,the relative scanning is performed by moving the wafer W with respect tothe exposure area IF which does not make movement), it is possible toquickly drive the wafer surface position into the image formation planeof the projection optical system PL by performing the pre-measurementcontrol. Thus, it is possible to perform quick and highly accuratefocus/leveling control. As for the method for the change, it ispreferable to perform grouping as described above, or it is preferableto always monitor the outputs of all of the sensors to use the detectingpoint which comes within an allowable value.

FIG. 39 resides in the “AF sensor number and position variable type” inwhich all detecting points are used provided that the measurement can beperformed therefor, regardless of the number of the AF detecting pointsto be used. This procedure is characterized in that the averaging effectis enhanced owing to the use of a plurality of AF detecting points,making it possible to be scarcely affected by camber or the likepossibly existing at the outer circumferential portion of the wafer. Forexample, when the reproducibility is unsatisfactory in the AFmeasurement, this effect is further enhanced. In the case of theprocedure shown in FIG. 39, like in FIG. 38, the main control unit 90also makes control so that the AF detecting points are changed on thebasis of positional information on the outer circumference of the wafer,positional information on the AF detecting points, and positionalinformation on the shot area as the exposure objective, in order torecognize what AF detecting point overlaps the effective area locatedinside the prohibition zone defined at the circumferential edge portionof the wafer W, while moving the wafer Win the scanning direction. Inthis procedure, the number of the AF detecting points is not limited.Therefore, the AF/AL measurement is performed by using all of thedetecting points included in the effective area, of the detecting pointsAF1 to AF9. Accordingly, even when the shot area located in the vicinityof the outer circumferential of the wafer W is subjected to scanningexposure from the outside to the inside, it is possible to quickly drivethe wafer surface position into the image formation plane of theprojection optical system PL by performing the pre-measurement control.Thus, it is possible to perform quick and highly accurate focus/levelingcontrol.

The use of the pre-measurement control method as described above may beused to make addition to the technique described, for example, inJapanese Laid-Open Patent Publication No. 6-283403 corresponding to U.S.Pat. No. 5,448,332. Thus, it is possible to perform quick and highlyaccurate scanning exposure for the respective shot areas on the wafersurface in accordance with the most rapid exposure order, regardless ofclassification of shot areas into those located inside the wafer andthose located in the vicinity of the outer circumference of the wafer.

Next, explanation will be made for what data are adopted aspre-measurement data when the pre-measurement control is performed asdescribed above. It is assumed, for example, that the width of theexposure area IF in the scanning direction is 6 to 8 mm, and thescanning velocity of the wafer during the exposure is 80 to 90 mm/sec.While being affected by the waviness frequency of the wafer surface, itis desirable for the throughput to give a relationship of theacceleration until the pre-measurement AF detecting point arrives at thewafer scanning velocity during exposure+the adjustment distance (L=8 to10 mm), in a degree corresponding to the absence of unnecessary run-up.This procedure is executed as follows. That is, the pre-measurementposition is calculated from information in the data file on the positionof the outer circumference of the wafer, the coordinate position of theshot area, and the distance L from the exposure area IF to the AFdetecting point. When the pre-measurement start position is locatedinside the pattern prohibition zone (usually about 30 mm; see FIG. 30)at the outer circumference of the wafer, the sensor correspondingthereto is adopted. However, the outer circumference of the wafer tendsto be affected by camber and dust. Even in the case of thepre-measurement start position set in the data file, the position doesnot necessarily represent the accurate position of the wafer surface.

Explanation will now be made for the procedure in which the controlerror caused in the aforementioned case is made as small as possible,with reference to FIGS. 40 and 41. In FIG. 40, it is assumed that, forexample, when the AF detecting points AF6 to AF9 are used as in thegroup C in the “AF detecting point fixation method” described above, thepre-measurement control start coordinate is located at a position (1)shown in FIG. 41 according to calculation based on the use of the datafile, however, the position (1) is affected by the pattern prohibitionzone, and it fairly suffers from de-focusing. In this case, as shown inFIG. 41, when the pre-measurement control is started at the position(1), the output values of the respective sensors are affected by thedetecting point AF6. If the result of measurement obtained by thepre-measurement involves a sizeable error with respect to the target, itseriously affects the leveling control, because the corresponding sensoris disposed at the most right end of the AF detecting points.

If the system is designed such that the pre-measurement point is movedat 80 mm/sec, and 70% thereof can be subjected to control duringscanning, and if the detecting point AF6 disposed at the most right endinvolves an error of not more than several μm in the Z axis direction,then the system merely suffers from a small error owing to the averagingeffect obtained during the pre-measurement control. However, if there isan error of several tens μm in the Z axis direction, and if the levelingcontrol is performed by using, as a target value, a result obtained byadding such a value including the error, then an error of an unallowabledegree is produced. For this reason, it is desirable that thepre-measurement is started when the result obtained by monitoring dataupon the start of the measurement for the pre-measurement detectingpoint is within an allowable range, while when the result exceeds theallowable range, the measurement result obtained by the pre-measurementcontrol is not used until arrival at the point (2) at which the resultis within the allowable range.

In the case of the “AF sensor position movement type” and the “AF sensornumber and position variable type” described above, it is possible touse only the AF detecting points included in the allowable range.

Further, a certain allowable range may be also set for the measurementerror concerning the respective detecting points, and the AF detectingpoints except for the AF detecting point which involves a cause toexceed the allowable range may be used. By doing so, for example, it ispossible to decrease the frequency of occurrence of AF error caused bythe influence of dust or the like attached to the back surface side ofthe wafer. However, in such a method, it is necessary to allow the wafersurface to be previously included within an allowable range with respectto the position for making driving into the target AF. Therefore, it isnecessary to execute global AF or global AF/AL beforehand on the basisof the result of focus measurement during the wafer alignment.

As explained above, according to the projection exposure apparatus 214concerning the fourth embodiment of the present invention, a pluralityof AF detecting points are arranged for the area which is wider in thenon-scanning direction than the exposure area IF on the wafer W, whenthe pattern on the reticle R is subjected to the scanning exposure ontothe wafer W by the aid of the projection optical system PL. Further,prior to the exposure for the shot area 212 located in the vicinity ofthe outer circumference of the wafer W, the pre-measurement for thefocus is started at the point of time at which a part of the pluralityof AF detecting points overlap the surface of the wafer W. The focuscontrol is started on the basis of the result of the measurement.Accordingly, the focus information on those located at the inside, whichhas not been able to be measured by using the pre-measurement controlbased on the use of the conventional scanning type projection exposureapparatus, can be used for the focus control as the pre-measurementdata. Therefore, it is possible to perform the highly accurate focuscontrol without deteriorating the throughput.

When one AF detecting point on the surface of the wafer W, of theplurality of AF detecting points is used, the leveling control duringthe exposure is performed by using the leveling information on theadjacent shot, or by using the fixed value (for example, both of theinclination amount in the X direction and the inclination amount in theY direction are “0”). Accordingly, the pre-measurement control can bestarted even for the incomplete shot area located in the vicinity of theouter circumference of the wafer.

Further, upon execution of the pre-measurement control by using onepoint of the AF detecting point on the surface of the wafer W, when theAF detecting point different from the aforementioned point overlaps thesurface of the wafer W, the pre-measurement is started at thecorresponding position. When the leveling control can be performed byusing the both results of the pre-measurement until the start ofexposure, the leveling process based on the use of the adjacent shot orthe leveling correction process based on the use of the fixed value asdescribed above is changed to the leveling control process based on thepre-measurement for the inside of the shot. By doing so, even in thecase of the pre-measurement control for the incomplete shot located atthe outer circumference portion, it is possible to perform thefocus/leveling control highly accurately.

The AF detecting points to be used when the pre-measurement is performedare determined on the basis of the positional information on the outercircumference of the wafer W, the positional information on theplurality of the AF detecting points, and the coordinate positions ofthe shot areas on the wafer W, at the point of time at which the shotarray on the wafer W is determined. Alternatively, the detection processbased on the use of the AF detecting points to be used for thepre-measurement control is always executed during the scanning for thewafer. The pre-measurement control is started from the point of time atwhich the detection result obtained at any of the detecting points iswithin the allowable value. Accordingly, even if the influence of theouter circumferential edge of the wafer is unexpectedly larger than thatassumed from the designed coordinate, the focus control is not startedat that point of time. Therefore, it is possible to avoid occurrence ofa large focus/leveling error.

In the fourth embodiment described above, explanation has been made forthe case in which one wafer stage is used. However, it is a matter ofcourse that the present invention can be carried out in the case of theuse of two stages as explained in the first to the third embodiments. Inthis case, it is not necessarily indispensable to previously perform thefocus measurement by using the alignment system. However, for thepurpose of higher accuracy, it is preferable to perform the focusmeasurement by using the alignment system. When the focus alignmentbased on the use of the alignment system is not performed, an advantageis obtained in that the operation time therefor can be used for theoperation time for other purposes.

[Fifth Embodiment]

The fifth embodiment of the present invention will now be described withreference to FIGS. 44 to 47.

FIG. 44 shows the constitution of an exposure apparatus 100 related tothe first embodiment. This exposure apparatus 100 is a step-and-repeatreduced projection exposure apparatus (a so-called stepper).

The projection exposure apparatus 100 comprises an illumination systemIOP, a reticle stage RST for holding a reticle R as a mask, a projectionoptical system PL for projecting the image of a pattern formed in thereticle R onto a wafer W as a sensitive substrate, a wafer stage WS1 asa first substrate stage movable on a base 12 in a two-dimensionaldirection XY while holding the wafer W, a wafer stage WS2 as a secondsubstrate stage movable on the base 12 in the two-dimensional directionXY independently of the wafer stage WS1 while holding the wafer W, aninterferometer system 26 for measuring the positions of the two waferstages WS1, WS2, and a main controller 28 as controller comprising aminicomputer (or a microcomputer) including CPU, ROM, RAM and I/Ointerface, for supervising and controlling the entire apparatus.

The illumination system IOP is composed of a light source (mercury lampor excimer laser), and an illumination optical system comprising a flyeye lens, a relay lens, and a condenser lens. This illumination systemIOP illuminates a pattern of the lower surface of the reticle R (patternformation surface) with a uniform illuminance distribution byillumination light IL for exposure from the light source. Theillumination light IL for exposure used is an emission line such asi-line from a mercury lamp, or excimer laser light from, say, KrF orArF.

Onto the reticle stage RST, the reticle R is fixed via fixing means (notshown). The reticle stage RST is finely drivable by a driving system(not shown) in an X-axis direction (the right-and-left direction in thesheet face of FIG. 44), a Y-axis direction (the direction perpendicularto the sheet face of FIG. 44), and a θ direction (the direction ofrotation in the XY plane). This measure enables the reticle stage RST toperform positioning of the reticle R (reticle alignment) such that thecenter of the pattern of the reticle R (the reticle center) practicallyagrees with the optical axis Ae of the projection optical system PL. InFIG. 44, the state in which this reticle alignment has been performed isillustrated.

The projection optical system PL has the optical axis Ae lying in aZ-axis direction perpendicular to the moving plane of the reticle stageRST. Here, a both-sided telecentric system with a predeterminedreduction ratio β (β of, say, ⅕) is used. Thus, when the reticle R isilluminated at a uniform illuminance by the illumination light IL withthe pattern of the reticle R being aligned with the shot areas on thewafer W, the pattern on the pattern formation surface is reduced by theprojection optical system PL at the reduction ratio β. The so reducedpattern is projected onto the wafer W coated with a photoresist, wherebythe reduced image of the pattern is formed in each shot area on thewafer W.

In the instant embodiment, an X fixed mirror 14X serving as a referencefor X-axis direction position control during exposure of the waferstages WS1, WS2 is fixed to one side (left side in FIG. 44) surface ofthe projection optical system PL in the X-direction. Similarly, a Yfixed mirror 14Y serving as a reference for Y-axis direction positioncontrol during exposure of the wafer stages WS1, WS2 is fixed to oneside (rear side of the sheet face of FIG. 44) surface of the projectionoptical system PL in the Y-direction (see FIG. 46).

On the bottom surface of each of the wafer stages WS1, WS2, a gas staticpressure bearing (not shown) is provided. By these gas static pressurebearings, the wafer stages WS1, WS2 are supported floatingly above thebase 12 with a clearance of about several microns kept between them andthe upper surface of the base 12. One side (left side in FIG. 44)surface in the X-axis direction of each of the wafer stages WS1, WS2,and one side (rear side of the sheet face in FIG. 44) surface in theY-axis direction of each of the wafer stages WS1, WS2 are mirrorfinished to form reflecting surfaces that function as moving mirrors forreflecting a measuring beam from the interferometer system 26.

Onto the bottom surfaces of the wafer stages WS1, WS2, magnets arefixed. Under an electromagnetic force generated by driving coils (notshown) embedded in predetermined ranges of the base (concretely, apredetermined region near a site below the projection optical system PL,and a predetermined region near a site below the alignment microscopeWA), the wafer stages WS1, WS2 are moved on the base 12 in thetwo-dimensional direction XY. That is, the magnets on the bottomsurfaces of the wafer stages WS1, WS2 and the driving coils embedded inthe base 12 constitute a so-called moving magnet type linear motor asdriving means for the wafer stages WS1, WS2. The driving current of thedriving coils of this linear motor is controlled by the main controller28.

On the wafer stages WS1, WS2, wafers W are held by vacuum suction or thelike via wafer holders (not shown). Onto the wafer stages WS1, WS2, too,reference mark plates FM1, FM2 whose surface is as high as the surfaceof the wafer W are fixed. On the surface of the reference mark plateFM1, as shown in the plan view of FIG. 45, a mark WM for measurementwith a wafer alignment microscope WA to be described later on is formedat the center in the longitudinal direction of the surface. On bothsides of the mark WM in the longitudinal direction, a pair of marks RMare formed for use in measuring the relative positional relation withthe reticle R via the projection optical system PL. On the otherreference mark plate FM2, exactly the same marks WM, RM are formed.

In the instant embodiment, moreover, an off-axis alignment microscope WAas an alignment system for detecting a position detecting mark(alignment mark) formed on the wafer W is provided at a predetermineddistance of, say, 3,000 mm from the objection optical system PL in adirection at an angle of nearly 45° to the XY axis. The wafer W haslevel differences formed by exposure and processing for the previouslayers. They include position detecting marks (alignment marks) formeasurement of the positions of shot areas on the wafer. These alignmentmarks are measured by the alignment microscope WA.

The alignment microscope WA used here is an FIA (field image alignment)type alignment microscope relying on image processing. According to thismicroscope, illumination light emitted from a light source (not shown)which produces broad band illumination light, such as a halogen lamp, iscast on the wafer W (or the reference mark plate FM) after passing anobjective lens (not shown). Reflected light from a wafer mark region(not shown) on the surface of the wafer W passes sequentially throughthe objective lens and an indicator plate (not shown), forming an imageof the wafer mark and an image of the indicator on the indicator plateon an imaging surface of a CCD or the like (not shown). Photoelectricconversion signals of these images are processed by a signal processingcircuit (not shown) in a signal processing unit 160. The relativepositional relation between the wafer mark and the indicator iscalculated by a computing circuit (not shown), and this relativepositional relation is conveyed to the main controller 28. The maincontroller 28 calculates the position of the alignment mark on the waferW on the basis of the relative positional relation and the measuredvalues of the interferometer system 26.

To one side (left side in FIG. 44) surface of the alignment microscopeWA in the X-axis direction, an X fixed mirror 18X is fixed for servingas a reference for position control in the X-axis direction during thealignment action of the wafer stages WS1, WS2. Similarly, to one side(rear side of the sheet face of FIG. 44) surface of the alignmentmicroscope WA in the Y-axis direction, a Y fixed mirror 18Y is fixed forserving as a reference for position control in the Y-axis directionduring the exposure action of the wafer stages WS1, WS2.

Available as the alignment microscope are not only the FIA type, butother optical alignment devices such as LIA (laser interferometricalignment) or LSA (laser step alignment) devices, other optical devicessuch as a phase contrast microscope and a differential interferencemicroscope, and non-optical devices such as STM (scanning tunnelmicroscope) for detecting the atomic-level irregularities of the surfaceof a specimen by utilizing the tunnel effect, and AFM (atomic forcemicroscope) for detecting the atomic- and molecular-level irregularitiesof the surface of a specimen by utilizing atomic force (gravity,repulsion).

In the projection exposure apparatus 100 of the instant embodiment,reticle alignment microscopes 52A, 52B as mark detecting system forsimultaneously observing an image of the reference mark RM on thereference mark plate FM and a reticle alignment mark (not shown) on thereticle R through the projection optical system PL are provided abovethe reticle R. Detection signals S1, S2 from the reticle alignmentmicroscopes 52A, 52B are supplied to the main controller 28. In thiscase, deflecting mirrors 54A, 54B for guiding detection light from thereticle R to the reticle alignment microscopes 52A, 52B are unitizedintegrally with the relevant reticle alignment microscopes 52A, 52B toconstitute a pair of microscope units 56A, 56B. Upon start of anexposure sequence, these microscope units 56A, 56B are retreated by amirror driving device (not shown) to positions beyond the reticlepattern surface under a command from the main controller 28.

Next, the interferometer system 26 of FIG. 44 which manages thepositions of the wafer stages WS1, WS2 will be described in detail.

This interferometer system 26, actually, is composed of a first laserinterferometer 26Xe for X-axis direction position measurement, a secondlaser interferometer 26Ye for Y-axis direction position measurement, athird laser interferometer 26Xa for X-axis direction positionmeasurement, and a fourth laser interferometer 26Ya for Y-axis directionposition measurement, as illustrated in FIG. 46. These components arerepresentatively shown in FIG. 44 as the interferometer system 26.

The first laser interferometer 26Xe projects onto the X fixed mirror 14Xa reference beam X_(e1) in the X-axis direction that passes through thecenter of projection of the projection optical system PL. The firstlaser interferometer 26Xe also projects a measuring beam X_(e2) onto thereflecting surface of the wafer stage (WS1 or WS2). Reflected lightwaves from these two beams are superposed into one for interference.Based on this interference state, the displacement of the reflectingsurface of the wafer stage relative to the fixed mirror 14X is measured.

The second laser interferometer 26Ye projects onto the Y fixed mirror14Y a reference beam Y_(e1) in the Y-axis direction that passes throughthe center of projection of the projection optical system PL. The secondlaser interferometer 26Ye also projects a measuring beam Y_(e2) onto thereflecting surface of the wafer stage (WS1 or WS2). Reflected lightwaves from these two beams are superposed into one for interference.Based on this interference state, the displacement of the reflectingsurface of the wafer stage relative to the fixed mirror 14Y is measured.

The third laser interferometer 26Xa projects onto the X fixed mirror 18Xa reference beam X_(a1) in the X-axis direction that passes through thecenter of detection of the alignment microscope WA. The third laserinterferometer 26Xa also projects a measuring beam X_(a2) onto thereflecting surface of the wafer stage (WS1 or WS2). Reflected lightwaves from these two beams are superposed into one for interference.Based on this interference state, the displacement of the reflectingsurface of the wafer stage relative to the fixed mirror 18X is measured.

The fourth laser interferometer 26Ya projects onto the Y fixed mirror18Y a reference beam Y_(a1) in the Y-axis direction that passes throughthe center of detection of the alignment microscope WA. The fourth laserinterferometer 26Ya also projects a measuring beam Y_(a2) onto thereflecting surface of the wafer stage (WS1 or WS2). Reflected lightwaves from these two beams are superposed into one for interference.Based on this interference state, the displacement of the reflectingsurface of the wafer stage relative to the fixed mirror 18Y is measured.

Here, the measuring axis of the first laser interferometer 26Xe thatconsists of the reference beam X_(e1) and the measuring beam X_(e2) iscalled the first measuring axis Xe. The measuring axis of the secondlaser interferometer 26Ye that consists of the reference beam Y_(e1) andthe measuring beam Y_(e2) is called the second measuring axis Ye. Themeasuring axis of the third laser interferometer 26Xa that consists ofthe reference beam X_(e1) and the measuring beam X_(e2) is called thethird measuring axis Xa. The measuring axis of the fourth laserinterferometer 26Ya that consists of the reference beam Y_(e1) and themeasuring beam Y_(a2) is called the fourth measuring axis Ya. The firstmeasuring axis Xe and the second measuring axis Ye intersect each otherperpendicularly at In the center of projection of the projection opticalsystem PL (consistent with the center of the optical axis Ae), while thethird measuring axis Xa and the fourth measuring axis Ya intersect eachother perpendicularly at the center of detection of the alignmentmicroscope WA. Because of this constitution, the position of the waferstage can be measured precisely in the direction of each measuring axis,without Abbe's error due to yawing or the like of the wafer stage, bothduring measurement of the position detecting mark on the wafer W(alignment mark) and during exposure of the wafer W with the pattern. Toraise the accuracy of measurement, it is more desirable to usetwo-frequency heterodyne interferometers as the above first to fourthlaser interferometers.

Returning to FIG. 44, the measured values of the interferometer system26 are supplied to the main controller 28. The main controller 28controls the positions of the wafer stages WS1, WS2 via theaforementioned linear motors while monitoring the measured values of theinterferometer system 26.

As clear also from FIG. 46, the instant fifth embodiment is constructedsuch that during the exposure of the wafer W on the wafer stage WS1 orWS2 with the reticle pattern through the projection optical system PL,the position of the wafer stage is managed by the first and second laserinterferometers 26Xe, 26Ye. During the measurement of the positiondetecting mark on the wafer W (alignment mark) by the alignmentmicroscope WA, on the other hand, the position of the wafer stage ismanaged by the third and fourth laser interferometers 26Xa, 26Ya. Aftercompletion of the exposure, or after completion of the alignment markmeasurement, however, each measuring axis does not hit the reflectingsurface of each wafer stage. Thus, the positional control of the waferstage by the interference system 26 becomes difficult.

The projection exposure apparatus 100 of the instant embodiment,therefore, has a first robot arm 201 as a moving device for freelymoving the wafer stage WS1 among three locations, i.e., a third positionindicated by a virtual line in FIG. 46, a second position indicated by asolid line in FIG. 46, and a first position at which the wafer stage WS2is located in FIG. 46; and a second robot arm 221 as a moving device forfreely moving the wafer stage WS2 similarly among the three locations,the first position, the second position and the third position. Thesefirst and second robot arms 201, 221 are also controlled by the maincontroller 28, and the wafer stage position control accuracy of thesefirst and second robot arms 201, 221 is generally about +1 Mm. As theserobot arms 201, 221, articulated robot arms of a known structure areused, and their detailed description is omitted. To realize thatposition control accuracy without fail, upward/downward moving pins asillustrated by the numerals 24A, 24B in FIG. 46 may be provided asstoppers.

A brief explanation for the third, second and first positions will beoffered here. The third position refers to a wafer replacement positionat which the wafer W is passed on between a carrier arm 500 constitutingpart of an external substrate carrier mechanism and the wafer stage(WS1, WS2). The second position refers to a position at which thealignment of the wafer W on the wafer stage is performed after loadingof the wafer W is completed, and also an arbitrary position at which thethird measuring axis Xa and the fourth measuring axis Ya both hit thereflecting surfaces of the wafer stage. The first position refers to aposition at which the exposure of the wafer W on the wafer stage isperformed after alignment of the wafer is completed, and also anarbitrary position at which the first measuring axis Xe and the secondmeasuring axis Ye both hit the reflecting surfaces of the wafer stage.

In the instant embodiment, as described above, the positions illustratedin FIG. 46 are determined as the first, second and third positions.However, the second position may be any position if it satisfies theabove-mentioned definition. For example, a position at which the mark WMon the reference mark plate FM rests in the detection area of thealignment microscope WA may be set as the second position. Likewise, thefirst position may be any position if it satisfies the above-mentioneddefinition. For example, a position at which the mark RM on thereference mark plate FM rests in the projection area of the projectionoptical system PL may be set as the first position.

The following is an explanation for the overall flow of actions of theprojection exposure apparatus 100 of the instant embodiment constructedas stated above.

{circle around (1)} Assume that the wafer stage WS1 lies at the thirdposition, while the wafer stage WS2 lies at the first position.

First of all, wafer replacement is performed between the wafer stage WS1and the carrier arm 500. This wafer replacement is carried out by acenter lifting (wafer lifting) mechanism above the wafer stage WS1 andthe carrier arm 500 as done in the above-mentioned embodiment. Thus, adetailed description is omitted. As stated previously, the positioningaccuracy of a robot arm is generally abut ±1 μm or less, so that thepositioning accuracy of the carrier arm 500 is also comparable to thisvalue. Prior to this wafer replacement, the wafer W has roughly beenpositioned by a prealignment device (not shown) in the directions of X,Y and θ. Thus, its position of loading on the wafer stage does notdeviate markedly. The loading position of the wafer W relative to thereference mark plate FM1, for example, is within the error of ±1 μm orless.

During the wafer replacement, the wafer stage WS1 is notposition-controlled by a laser interferometer. However, the first robotarm 201 grasps the wafer stage WS1, so that the disadvantage of thewafer stage WS1 wandering about does not occur. During the grasp by thefirst robot arm 201, the linear motor that drives the wafer stage WS1 isat a halt (the same holds in the following description).

Upon completion of wafer replacement (loading of the wafer W onto thewafer stage WS1), the main controller 28 controls the first robot arm201 to move the wafer stage WS1 to the second position indicated by thesolid line in FIG. 46. At this position, the main controller 28 resetsthe third and fourth laser interferometers 26Xa, 26Ya simultaneously.Upon completion of this resetting, the first robot arm 201 finishes itsrole. Thus, the first robot arm 201 is retreated, away from the waferstage WS1, by a drive system (not shown) to a non-interfering positionin accordance with a command from the main controller 28.

After resetting of the third and fourth laser interferometers 26Xa, 26Yais completed, the main controller 28 controls the wafer stage WS1 viathe aforementioned linear motor, while monitoring the measured values ofthe interferometers 26Xa, 26Ya, so that the mark WM on the referencemark plate FM1 on the wafer stage WS1 is positioned in the detectionarea of the alignment microscope WA. The accuracy of positioning to thesecond position by the first robot arm 201 can be generally about ±1 μmor less, as stated earlier. Since the interferometric measuring axeshave been reset at this second position, position control can beperformed afterwards with a resolving power of about 0.01 μm on thebasis of the design value (the relative positional relation in designbetween the reflecting surface of the wafer stage WS1 and the mark WM onthe reference mark plate). As a result, the wafer stage WS1 ispositioned with sufficient accuracy for measurement of the mark WM bythe alignment microscope WA. When the second position is set at aposition at which the mark WM on the reference mark plate FM1 on thewafer stage WS1 is positioned in the detection area of the alignmentmicroscope WA, the movement of the wafer stage WS1 after resetting ofthe interferometers is not necessary. This is more desirable from theaspect of throughput.

Then, the alignment microscope WA measures the position of the mark WM(ΔW_(X), ΔW_(Y)) on the reference mark plate FM1 relative to the centerof detection (center of indicator) of the alignment microscope WA. Themain controller 28 obtains the average values (X₀, Y₀) of the measuredvalues of the third and fourth laser interferometers 26Xa, 26Ya duringthis measurement. The outcome shows that when the measured values of thelaser interferometers 26Xa, 26Ya show (X₀−ΔW_(X), Y₀−ΔW_(Y)) the mark WMon the reference mark plate FM1 lies directly below the center ofdetection (center of indicator) of the alignment microscope WA. A seriesof actions of the third and fourth laser interferometers 26Xa, 26Ya willbe called W-SET in the following description.

While wafer replacement, interferometer resetting, and a series ofactions of the W-SET are being performed on the one wafer stage, WS1, inthe above manner, the actions described below are carried out on theother wafer stage, WS2.

That is, the wafer stage WS2 is moved to the first position by thesecond robot arm 221 as described previously. The control forpositioning to the first position is also performed with an accuracy of±1 μm or less. At the same time that the movement of the wafer stage WS2to the first position is completed, the main controller 28 resets thefirst and second laser interferometers 26Xe, 26Ye.

Upon completion of this resetting by the first and second laserinterferometers 26Xe, 26Ye, the second robot arm 221 finishes its role.Thus, the second robot arm 22 is retreated, away from the wafer stageWS2, by a drive system (not shown) to a non-interfering position inaccordance with a command from the main controller 28.

Then, the main controller 28 controls the position of the wafer stageWS2 via the linear motor, while monitoring the measured values of thelaser interferometers 26Xe, 26Ye, so that the mark RM on the referencemark plate FM2 is positioned at a position at which it overlaps via theprojection optical system PL the reticle alignment mark (not shown)formed on the reticle R in the projection area of the projection opticalsystem. In this case, the accuracy of positioning to the first positionby the second robot arm 22 can be generally about ±1 μm or less, asstated earlier. Since the interferometric measuring axes have been resetat this first position, position control can be performed afterwardswith a resolving power of about 0.01 μm on the basis of the designvalues (the relative positional relation in design between thereflecting surfaces of the wafer stage WS2 and the marks RM on thereference mark plate FM2). As a result, the wafer stage WS2 ispositioned with necessary and sufficient accuracy for the simultaneousobservation of the reticle alignment mark and the mark RM on thereference mark plate FM by the reticle alignment microscopes 52A, 52B.

Then, the reticle alignment microscopes 52A, 52B measure the relativespacings (ΔR_(X), ΔR_(Y)) between the reticle alignment mark on thereticle R and the mark RM on the reference mark plate FM2, namely, thepositional deviations (ΔR_(X), ΔR_(Y)) of the center of the referencemark RM as the reference point on the wafer stage WS2 from the center ofprojection of the pattern image of the reticle R as the predeterminedreference point in the projection area of the projection optical systemPL. The main controller 28 takes in these measured values of the reticlealignment microscopes 52A, 52B, and simultaneously read the measuredvalues (X₁, Y₁) of the laser interferometers 26Xe, 26Ye. The resultsshow that the positions at which the measured values of the laserinterferometers 26Xe, 26Ye become (X₁−ΔR_(X), Y₁−ΔR_(Y)) are thepositions at which the reticle alignment mark and the mark RM on thereference mark plate FM2 just overlap each other via the projectionoptical system PL. This series of actions after resetting of the firstand second laser interferometers 26Xe, 26Ye will be called R-SET in thefollowing description.

{circle around (2)} Then, wafer alignment on the wafer stage WS1 sideand exposure on the wafer stage WS2 side are performed in parallel.

After resetting of the third and fourth laser interferometers 26Xa,26Ya, the position of the wafer stage WS1 is managed based on themeasured values of the laser interferometers 26Xa, 26Ya. The maincontroller 28 measures the positions of the position detecting marks(alignment marks) for predetermined specific sample shots among aplurality of shot areas on the wafer W. The main controller 28 measuresthese positions on the (Xa, Ya) coordinate system based on output fromthe alignment microscope WA, by moving the wafer stage WS1 sequentiallyvia the linear motor, while monitoring the measured values of theinterferometers 26Ya, 26Xa. In this case, the measured values of theinterferometers (X₀−Δ_(X), Y₀−Δ_(Y)) when the mark WM on the referencemark plate FM1 comes directly below the center of detection of thealignment microscope WA have been obtained. Based on these values andthe design values for the relative positions of each alignment mark tothe reference mark WM, it is determined by computation what the measuredvalues of the laser interferometers 26Ya, 26Xa should be in order toposition each alignment mark on the wafer W in the detection area of thewafer alignment microscope WA, and what position the wafer stage WS1should be moved to in order to achieve those values. Based on theresults of these computations, the wafer stage WS1 is movedsequentially.

To position the wafer W in the directions of X, Y and θ, it suffices tomeasure, at least, two X measurement marks and one Y measurement mark(or one X measurement mark and two Y measurement marks). Here, three ormore X measurement marks not on a straight line, and three or more Ymeasurement marks not on a straight line should be measured as EGAsample shots.

The measured alignment mark (wafer mark) positions of the respectivesample shots and the data on arrangement of the designed shot areas areused to perform statistical calculation by the least-squares method asdisclosed in Japanese Laid-Open Patent Publication No. 61-44429,corresponding to U.S. Pat. No. 4,780,617, thereby obtaining all data onthe arrangement of the plurality of shot areas on the wafer W. However,it is desirable to subtract from the results of calculation theaforementioned value of the interferometers (X₀−Δ_(X), Y₀−Δ_(Y)), whichis obtained when the mark WM on the reference mark plate FM1 comesdirectly below the center of detection of the alignment microscope WA,so as to convert into data relative to the reference mark MA on thereference mark plate FM1. This measure gives a necessary and sufficientknowledge of the relative positional relation between the mark WM on thereference mark plate FM1 and the reference point of each shot area onthe wafer W.

In parallel with the fine alignment (EGA) on the wafer stage WS1 side,superposed exposure of the pattern image of the reticle R and a knownpattern of shot areas on the wafer W is performed on the wafer stage WS2side in the following manner:

That is, the main controller 28 positions each shot area on the wafer Win the exposure position, while monitoring the measured values of theinterferometers 26Ye, 26Xe, based on the results of measurement of thepositional deviations, the coordinate position (Xe, Ye) of the waferstage WS2 at that time, and the coordinate data on the arranged shotsrelative to the reference mark WM on the reference mark plate FM2calculated in the same way as in the alignment action. Performing thispositioning, the main controller 28 exposes the wafer W with the reticlepattern sequentially in the step-and-repeat manner, while controllingthe opening and closing of the shutter in the illumination opticalsystem. Here, high precision superposition is possible although theinterferometers 26Xe, 26Ye are reset (the measuring axes of theinterferometers are interrupted) prior to the exposure of the wafer W onthe wafer stage WS2. Detailed reasons for this are as follows: Thespacing between the mark WM and the mark RM on the reference mark plateFM2 is known. As a result of fine alignment (EGA) performed previously,the relative positional relation between the mark WM on the referencemark plate FM2 and the reference point of each shot area on the wafer Whas been calculated in the same manner as described earlier. Also, ithas been measured where on the wafer stage WS2 the reticle alignmentmark on the reticle R is situated (namely, what is the relativepositional relation between the center of projection of the patternimage of the reticle (almost consistent with the center of projection ofthe projection optical system PL) as the predetermined reference pointin the projection area of the projection optical system PL and the markRM as the reference point on the wafer stage WS2). Based on the resultsof these measurements, it is clear what measured values of the first andsecond laser interferometers 26Xe, 26Ye result in the exactsuperposition of the pattern image of the reticle R with each shot areaon the wafer W.

{circle around (3)} In the foregoing manner, fine alignment (EGA) iscompleted on the wafer stage WS1 side, while exposure with the reticlepattern for all the shot areas on the wafer W is completed on the waferstage WS2 side. Then, the wafer stage WS1 is moved to the first positionbelow the projection optical system PL, while the wafer stage WS2 ismoved to the third position, the position of wafer replacement.

In detail, the wafer stage WS1 is grasped by the first robot arm 201 andmoved to the first position in accordance with an instruction from themain controller 28. The control for positioning to the first position isperformed with an accuracy of ±1 μm or less. Simultaneously with thecompletion of movement of the wafer stage WS1 to the first position, themain controller 28 resets the first and second laser interferometers26Xe, 26Ye.

Upon completion of this resetting, the first robot arm 201 finishes itsrole. Thus, the first robot arm 201 is retreated, away from the waferstage WS1, by the drive system (not shown) to a non-interfering positionin accordance with an instruction from the main controller 28.

Then, the main controller 28 carries out R-SET in the same manner as forthe wafer stage WS2 side stated earlier. This step results in themeasurement of the relative spacings (ΔR_(X), ΔR_(Y)) between thereticle alignment mark and the mark RM on the reference mark plate FM1,namely, the positional deviations (ΔR_(X), ΔR_(Y)) of the center of thereference mark RM as the reference point on the wafer stage WS2 from thecenter of projection of the pattern image of the reticle R as thepredetermined reference point in the projection area of the projectionoptical system PL, as well as the stage coordinate position (X₁, Y₁) atthe time of measuring the positional deviations.

While the interferometer resetting and the R-SET are being performed onthe wafer stage WS1 side in the above manner, the second robot arm 221grasps the wafer stage WS2, whose exposure action has been completed, inaccordance with an instruction from the main controller 28. The secondrobot arm 22 moves this wafer stage WS2 to the wafer passing-on position(third position) for wafer replacement. Then, wafer replacement,interferometer resetting and W-SET are performed in the same manner ason the wafer stage WS1 side that has been mentioned previously.

{circle around (4)} Then, the main controller 28, as stated earlier,controls the actions of the wafer stages WS1 and WS2 so that finealignment (EGA) is performed on the wafer stage WS2 side, while thewafer W is sequentially exposed with the reticle pattern by thestep-and-repeat method on the wafer stage WS1 side in parallel with EGA.

{circle around (5)} Thereafter, the main controller 28 controls theactions of the stages WS1, WS2 and the actions of the first and secondrobot arms so that the actions of {circle around (1)} to {circle around(4)} explained above will be repeated in sequence.

A flow of the above-described parallel actions taking place on the twostages, WS1 and WS2, is illustrated in FIG. 47.

As described above, the projection exposure apparatus 100 related to thefifth embodiment can perform an exposure action on one of the waferstage WS1 and the wafer stage WS2, and a fine alignment action on theother stage in parallel. Thus, throughput can be expected to improvemarkedly in comparison with earlier technologies by which waferreplacement (including search alignment), fine alignment and exposurewere performed sequentially. This is because a fine alignment action andan exposure action account for a high proportion of the time requiredfor an exposure sequence.

The above embodiment also makes it a precondition that the measuringaxes of the interferometer system 26 are interrupted. Thus, it sufficesfor the reflecting surface (a moving mirror, if any) of each wafer stageto be slightly longer than the wafer diameter. Compared with earliertechnologies requiring uninterrupted measuring axes, therefore, thewafer stage can be compact and light-weight, so that an improvement instage controlling performance can be expected.

The embodiment, moreover, makes it a precondition that the measuringaxes of the interferometer system are interrupted, and the position ofthe mark on the reference mark plate FM on the stage is measured eachbefore alignment and exposure. Thus, it produces no disadvantage howeverlong the center distance (baseline amount) between the center ofprojection of the projection optical system PL and the center ofdetection of the alignment microscope WA will be. By providing asomewhat large spacing between the projection optical system PL and thealignment microscope WA, wafer alignment and exposure can be performedin a time-parallel manner, with no interference between the wafer stageWS1 and the wafer stage WS2.

In the above embodiment, furthermore, the interferometer system 26 hasthe first measuring axis Xe and the second measuring axis Yeintersecting perpendicularly at the center of projection of theprojection optical system PL, and the third measuring axis Xa and thefourth measuring axis Ya intersecting perpendicularly at the center ofdetection of the alignment system WA. Thus, the two-dimensional positionof the wafer stage can be managed accurately both during an alignmentaction and during exposure.

In addition, the fixed mirrors 14X, 14Y, 18X, 18Y for interferometersare fixed to the side surfaces of the projection optical system PL andthe side surfaces of the alignment microscope WA. Unless the positionsof the fixed mirrors change during alignment and exposure, therefore,disadvantages, such as a fall in the position control accuracy of thewafer stage, will not emerge, even if the positions of the fixed mirrorschange owing to changes over time or vibrations of the apparatus. Thus,constructing the alignment microscope WA so as to be movable upward anddownward would not cause any disadvantage.

The foregoing fifth embodiment has been described such that the waferstages WS1 and WS2 are moved by the first and second robot arms 201, 221among three locations, i.e., the first, second and third positions.However, the present invention is in no way limited to thisconstitution. If the wafer is replaced at the second position, forexample, the wafer stages WS1 and WS2 may be moved by the first andsecond robot arms 201, 221 between the first and second positions. Inthis case, the main controller 28 controls the actions of the waferstages WS1 and WS2 so that an exposure action for the wafer W on one ofthese stages and an alignment action for the wafer W on the other stageare performed in parallel. Then, the main controller 28 causes the firstand second robot arms 201, 221 to interchange the positions of bothstages.

The fifth embodiment has also been described such that step-and-repeattype exposure is performed for the wafer W on the stage on the basis ofEGA. However, the present invention is in no way limited to thisconstitution, and the pattern image of the reticle may be projectedsequentially onto each shot area on the wafer W with alignment andexposure being repeated die by die. In this case, the relative positionof each alignment mark relative to the mark WM formed on the referencemark plate FM on the stage is measured during alignment. Thus, thereticle pattern image can be superimposed on each shot area based onthis relative position in the same manner as described above. Such adie-by-die method is desirably adopted when the number of the shot areason the wafer W is small. If the number of the shot areas is large, theaforementioned EGA method is desirable from the point of view ofpreventing a decrease in throughput.

The fifth embodiment has also been described such that the first robotarm 201 moves one stage, WS1, among three locations, i.e., the first,second and third positions, while the second robot arm 221 moves theother stage, WS2, among the three locations, i.e., the first, second andthird positions. However, the present invention is in no way limited tothis constitution. It is permissible, for example, to employ a method bywhich one robot arm 201 carries the stage WS1 (or WS2) to a positionother than the first, second or third position and frees it there duringits carriage from the first position to the third position, while theother robot arm 221 moves this stage WS1 (or WS2) from this position tothe third position. This makes it possible to use one robot arm 201exclusively for carriage between the second and first positions of bothstages, and use the other robot arm 221 exclusively for carriage betweenthe third and second positions of both stages.

Also, each laser interferometer constituting the interferometer system26 may be a multi-axis interferometer which can measure not only therectilinear positions of the wafer stage in the X- and Y-direction, butalso its yawing or pitching.

[Sixth Embodiment]

Next, the sixth embodiment of the present invention will be describedwith reference to FIG. 48. The constituent parts identical with orcomparable to those in the fifth embodiment will be assigned the samenumerals or symbols, and their explanations will be omitted.

The sixth embodiment is characterized in that a wafer stage WS1 isconstituted to be divisible into two parts, i.e., a stage body WS1 a anda substrate holding member WS1 b detachably mounted on the stage bodyWS1 a and having the same shape as the stage body WS1 a; and thatlikewise, a wafer stage WS2 is constituted to be divisible into twoparts, i.e., a stage body WS2 a and a substrate holding member WS2 bdetachably mounted on the stage body WS2 a and having the same shape asthe stage body WS2 a.

On the substrate holding members WS1 b, WS2 b, the wafer W is held bysuction via a wafer holder (not shown). Reflecting surfaces functioningas moving mirrors for an interferometer are formed on the side surfacesthereof. On these substrate holding members WS1 b, WS2 b, reference markplates FM1, FM2 are provided, respectively, on their upper surfaces.

In this sixth embodiment, parallel processings are performed on thewafer stages WS1, WS2 in practically the same manner as in theaforementioned fifth embodiment. At a time when an alignment action iscompleted on one stage side, and an exposure action is completed on theother stage side, the main controller 28 controls a first and a secondrobot arm 201, 221. As a result, the substrate holding member WS1 b (orWS2 b) on the alignment-completed stage side is carried (moved) onto thestage body WS2 a that has stopped at the first position. In parallel,the substrate holding member WS2 b (or WS1 b) on the exposure-completedstage side is carried onto the stage body WS1 a that has stopped at thesecond position. In this manner, the substrate holding members WS1 b,WS2 b are replaced. During replacement of the substrate holding membersWS1 b, WS2 b, the measuring axes of an interferometer system 26 areinterrupted, making the position control of the wafer stages WS1, WS2impossible. During this period, stage stoppers 30 a, 30 b appear andhold the stage bodies WS1 a, WS2 a in place. In this case, waferreplacement is performed at the second position by a carrier arm (notshown).

In the instant sixth embodiment, as will be easily imagined from FIG.48, the position at which the mark WM on the reference mark plate FMlies in the detection area of the alignment microscope WA is determinedas the second position; whereas the position at which the mark RM on thereference mark plate FM lies in the projection area of the projectionoptical system PL is determined as the first position. Thus, the maincontroller 28 carries out the movement of the substrate holding membersWS1 b, WS2 b onto the stage bodies, resetting of the measuring axes ofthe interferometer system 26, and the R-SET or W-SET.

The sixth embodiment can obtain comparable effects to those by the fifthembodiment.

The sixth embodiment has been described such that the first and secondrobot arms 201, 221 move the substrate holding member between the firstand second positions. However, as in the first embodiment, the first andsecond robot arms 201, 221 may move the substrate holding member amongthree locations, i.e., the first, second and third positions. In thiscase, wafer replacement can be performed at a site unrelated to theprojection optical system PL or the alignment microscope WA. Hence, evenif the working distance below the alignment microscope WA is narrow, forexample, there are none of disadvantages such that the alignmentmicroscope WA impedes wafer replacement. The fifth and sixth embodimentshave been described such that robot arms or stage stoppers are used asmeasures during the interruption of the measuring axes of theinterferometer system 26. The present invention is not limited to thisconstitution. For instance, a two-dimensional grating may be formed onthe lower surface of the wafer stage, so that the position can be readby an optical encoder from below the stage travel surface.Alternatively, there may be employed means capable of precisely movingthe stage to a next position once the interferometer measuring axes areinterrupted, or means capable of holding the stage body at apredetermined position while stopping it there.

The fifth and sixth embodiments have also been described such that twowafer stages movable independently are provided. However, three or morewafer stages which are movable independently may be provided. If threewafer stages are provided, an exposure action, an alignment action, anda wafer flatness measuring action, for example, can be performed inparallel. There may be a plurality of the projection optical systems PLand alignment microscopes WA. If a plurality of the projection opticalsystems PL are present, an alignment action and two different patternsof exposure actions can be performed in parallel. This is suitable fordouble exposure or the like.

The above embodiments have been illustrated in which the presentinvention was applied to a step-and-repeat projection exposureapparatus. However, the range of application of this invention is notrestricted to this constitution. This invention is applicable not onlyto a step-and-scan projection exposure apparatus, but to other types ofexposure apparatuses, such as an electron beam direct drawing device.

INDUSTRIAL APPLICABILITY

As explained above, according to the projection exposure apparatus andthe projection exposure method of the invention, it possible to furtherimprove the throughput. According to the projection exposure apparatusand the projection exposure method of the invention, an excellenteffect, which has not been obtained in the conventional technique, isobtained in that it is possible to improve the throughput, miniaturizethe substrate stage, and reduce the weight of the substrate stage.

According to the projection exposure apparatus and the projectionexposure method of the invention, it is possible to further improve thethroughput and avoid any mutual influence of disturbance between twosubstrate stages.

According to the projection exposure apparatus and the projectionexposure method of the invention, it is possible to further improve thethroughput and avoid any mutual interference between the two substratestages. According the exposure method of the invention, it is possibleto improve throughput and determine the size of the substrate stageregardless of the baseline amount. According to the exposure apparatusof the invention, it is possible to improve throughput by the parallelexecution of an exposure action on one substrate stage and an alignmentaction on the other substrate stage.

According to the projection exposure apparatus and the projectionexposure method of the invention, it is possible to perform the highlyaccurate focus/leveling control while further improving the throughput.According to the projection exposure method of the invention, it ispossible to perform the highly accurate focus/leveling control whilefurther improving the throughput, even in the case of the use of EGA inwhich the positional adjustment is performed with respect to the mask onthe basis of the arrangement of the sample shot areas. According to theprojection exposure apparatus of the invention, it is possible toperform the highly accurate focus/leveling control while improving thethroughput, by using, as the pre-measurement data for the focus control,the focus information on those located at the inside which could not besubjected to pre-measurement when the shot areas located in the vicinityof the outer circumference of the sensitive substrate are exposed.

According to the scanning exposure method of the invention, it ispossible to perform the highly accurate focus/leveling control whilefurther improving the throughput. Therefore, the exposure apparatus andthe exposure method of the invention are extremely suitable forproducing semiconductor elements and liquid crystal display elements bymeans of the photolithography process.

What is claimed is:
 1. A projection exposure method for exposingsensitive substrates by projecting a pattern formed on a mask through aprojection optical system onto the sensitive substrates, comprising:preparing a first substrate stage and a second substrate stage, each ofwhich is movable independently on a two-dimensional plane while holdinga sensitive substrate; and performing, by using the first substratestage, at least one of an exchange operation for the sensitive substrateand a detecting operation for a mark on the first stage or on thesensitive substrate held on the first stage, while executing a scanningexposure operation for the sensitive substrate held on the secondsubstrate stage, wherein each of shot areas on the sensitive substrateheld on the second substrate stage is exposed by moving the secondsubstrate stage while projecting the pattern on the mask onto thesensitive substrate held on the second substrate stage, and wherein thetwo substrate stages are controlled such that the two substrate stagesdo not physically interfere with each other.
 2. The projection exposuremethod according to claim 1, wherein the operations of the two substratestages are switched between one another when the operations of the twosubstrate stages are completed.
 3. The projection exposure methodaccording to claim 2, wherein moving regions of the two substrate stagesare switched between one another when the operations of the twosubstrate stages are completed.
 4. The projection exposure methodaccording to claim 1, wherein the second substrate stage is preventedfrom vibration when the first substrate stage is moved.
 5. Theprojection exposure method according to claim 1, wherein a moving regionof the first substrate stage which executes the at least one of theexchange operation and the detection operation overlaps a moving regionof the second substrate stage which executes the scanning exposureoperation.
 6. A method for making a device, the method comprisingperforming a lithography process utilizing the method defined inclaim
 1. 7. The projection exposure method according to claim 1, whereinpredetermined information is stored to prevent the two substrate stagesfrom physically interfering with each other.
 8. The projection exposuremethod according to claim 1, wherein the first substrate stage is movedto sequentially detect a plurality of marks on the substrate held on thefirst substrate stage in the detecting operation.
 9. A projectionexposure method for exposing sensitive substrates by projecting an imageof a pattern formed on a mask via a projection optical system onto thesensitive substrates, comprising: preparing a first substrate stage anda second substrate stage, each of which moves independently on atwo-dimensional plane while holding a sensitive substrate; andsuccessively exposing, by projection, a plurality of portions on thesensitive substrate held on the first substrate stage with the image ofthe pattern formed on the mask, and successively detecting a pluralityof marks on the sensitive substrate held on the second substrate stageconcurrently therewith, wherein an order of the detection of the markson the sensitive substrate held on the second substrate stage isdetermined so that the two substrate stages do not physically interferewith each other.
 10. The projection exposure method according to claim9, wherein each of the portions on the sensitive substrate held on thefirst substrate stage is exposed with a scanning exposure operation. 11.The projection exposure method according to claim 9, wherein the firstsubstrate stage is prevented from vibration when the second substratestage is moved.
 12. A method for making a device, the method comprisingperforming a lithography process utilizing the method defined in claim2.
 13. A projection exposure method for exposing sensitive substrates byprojecting a pattern formed on a mask through a projection opticalsystem onto the sensitive substrates, comprising: preparing a firstsubstrate stage and a second substrate stage, each of which is movableindependently on a two-dimensional plane while holding a sensitivesubstrate; and performing, by using the first substrate stage, at leastone of an exchange operation for the sensitive substrate and a detectingoperation for a mark on the first substrate stage or on the sensitivesubstrate held on the first substrate stage, while executing an exposureoperation for the sensitive substrate held on the second substratestage, wherein a moving region of the first substrate stage whichexecutes the at least one of the exchange operation and the detectingoperation overlaps a moving region of the second substrate stage whichexecutes the exposure operation and wherein the two substrate stages arecontrolled such that the two substrate stages do not physicallyinterfere with each other.
 14. The projection exposure method accordingto claim 13, wherein the second substrate stage is prevented fromvibration when the first substrate stage is moved.
 15. The projectionexposure method according to claim 13, wherein predetermined informationis stored to prevent the two substrate stages from physicallyinterfering with each other.
 16. The projection exposure methodaccording to claim 13, wherein the first substrate stage is moved tosequentially detect a plurality of marks on the substrate held on thefirst substrate stage in the detecting operation.
 17. The projectionexposure method according to claim 13, wherein the operations of the twosubstrate stages are switched between one another when the operations ofthe two substrate stages are completed.
 18. The projection exposuremethod according to claim 17, wherein moving regions of the twosubstrate stages are switched between one another when the operations ofthe two substrate stages are completed.
 19. A method for making adevice, the method comprising performing a lithography process utilizingthe method defined in claim
 13. 20. A projection exposure apparatus forsequentially exposing sensitive substrates by projecting a patternformed on a mask illuminated with an exposure beam, the apparatuscomprising: a projection system, disposed in a path of the exposurebeam, which projects the pattern onto a sensitive substrate; a stagesystem, disposed on an image plane side of the projection system, whichhas a first substrate stage and a second substrate stage, each of whichis movable independently in a plane while holding a sensitive substrate;and a control system, functionally associated with the stage system,which controls the stage system to perform, by controlling the firstsubstrate stage, at least one of an exchange operation for the sensitivesubstrate and a detecting operation for a mark on the first substratestage or on the sensitive substrate held on the first substrate stage,while executing a scanning exposure operation for the sensitivesubstrate held on the second substrate stage, wherein each of shot areason the sensitive substrate held on the second substrate stage is exposedwhile moving the second substrate stage, and wherein the control systemcontrols the two substrate stages such that the two substrate stages donot physically interfere with each other.
 21. The projection exposureapparatus according to claim 20, further comprising: a detecting system,functionally connected with the control system, which detects the markon the first substrate stage or on the sensitive substrate held on thefirst substrate stage, wherein the detecting system sequentially detectsa plurality of marks on the sensitive substrate held on the firstsubstrate stage.
 22. The projection exposure apparatus according toclaim 21, wherein the control system performs statistical calculationbased on information detected by the detecting system to obtainpositional information of shot areas on the sensitive substrate held onthe first substrate stage.
 23. The projection exposure apparatusaccording to claim 21, wherein the detecting system includes a firstdetector to detect the marks on the sensitive substrate held on thefirst substrate stage and a second detector to detect a plurality ofmarks on the sensitive substrate held on the second substrate stage. 24.The projection exposure apparatus according to claim 20, furthercomprising: an interferometer system, functionally associated with thestage system and the control system, which has a plurality ofmeasurement axes and measures positions of the two substrate stages; anda linear motor system, magnetically connected to the two substratestages, which moves the two substrate stages based on the positionsmeasured by the interferometer system.
 25. The projection exposureapparatus according to claim 20, further comprising: an exchange system,functionally associated with the stage system and the control system,which includes a first exchanger which performs substrate transferbetween itself and the first substrate stage and a second exchangerwhich performs substrate transfer between itself and the secondsubstrate stage.
 26. The projection exposure apparatus according toclaim 20, wherein the control system stores information to prevent thetwo substrate stages from interfering with each other.
 27. Theprojection exposure apparatus according to claim 20, wherein a movingregion of the first substrate stage which executes the at least one ofthe exchange operation and the detecting operation overlaps a movingregion of the second substrate stage which executes the scanningexposure operation.
 28. The projection exposure apparatus according toclaim 20, wherein the second substrate stage is prevented from vibrationwhen the first substrate stage is moved.
 29. A projection exposureapparatus for sequentially exposing sensitive substrates by projecting apattern formed on a mask illuminated with an exposure beam, theapparatus comprising: a projection system, disposed in a path of theexposure beam, which projects the pattern onto a sensitive substrate; astage system, disposed on an image plane side of the projection system,which has a first substrate stage and a second substrate stage, each ofwhich is movable independently in a plane while holding a sensitivesubstrate; and a control system, functionally associated with the stagesystem, which controls the stage system to perform, by controlling thefirst substrate stage, at least one of an exchange operation for thesensitive substrate and a detecting operation for a mark on the firstsubstrate stage or on the sensitive substrate held on the firstsubstrate stage, while executing an exposure operation for the sensitivesubstrate held on the second substrate stage, wherein a moving region ofthe first substrate stage during the at least one of the exchangeoperation and the detecting operation overlaps a moving region of thesecond substrate stage of the two substrate stages during the exposureoperation, and wherein the control system controls the two substratestages such that the two substrate stages do not physically interferewith each other.
 30. The projection exposure apparatus according toclaim 29, further comprising: a detecting system, functionally connectedwith the control system, which detects the mark on the first substratestage or on the sensitive substrate held on the first substrate stage,wherein the detecting system sequentially detects a plurality of markson the sensitive substrate held on the first substrate stage.
 31. Theprojection exposure apparatus according to claim 30, wherein the controlsystem performs statistical calculation based on information detected bythe detecting system to obtain positional information of shot areas onthe sensitive substrate held on the first substrate stage.
 32. Theprojection exposure apparatus according to claim 30, wherein thedetecting system includes a first detector to detect the marks on thesensitive substrate held on the first substrate stage and a seconddetector to detect a plurality of marks on the sensitive substrate heldon the second substrate stage.
 33. The projection exposure apparatusaccording to claim 29, further comprising: an interferometer system,functionally associated with the stage system and the control system,which has a plurality of measurement axes and measures positions of thetwo substrate stages; and a linear motor system, magnetically connectedto the two substrate stages, which moves the two substrate stages basedon the positions measured by the interferometer system.
 34. Theprojection exposure apparatus according to claim 29, further comprising:an exchange system, functionally connected with the control system,which includes a first exchanger which performs substrate transferbetween itself and the first substrate stage and a second exchangerwhich performs substrate transfer between itself and the secondsubstrate stage.
 35. The projection exposure apparatus according toclaim 29, wherein the control system stores information to prevent thetwo substrate stages from interfering with each other.
 36. Theprojection exposure apparatus according to claim 29, wherein the secondsubstrate stage is prevented from vibration when the first substratestage is moved.